Initial checkin of Google Sign-In plugin for Unity.

This checkin includes the Android support.  The implementation uses
a Java implementation of an Android fragment to call the Auth methods.  This
java code is accessed from a native C++ layer, which is invoked via the PInvoke
API in Unity.

Change-Id: I6fbf978d5aff87b12039ab28f70c5a8ab336f96b

Author: claywilkinson

.gitignore

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+.gradle/
+.idea/
+bin/
+build/
+*.iml
+local.properties
+local.settings
+.externalNativeBuild/
+*.apk
+
+*.sln
+*.userprefs
+Library/
+ProjectSettings/
+Temp/
+obj/
+
+# Don't check in the resolver
+GoogleSignInPlugin/Assets/PlayServicesResolver/
+
+# don't checkin client plists
+GoogleSignInPlugin/Assets/Plugins/iOS/client*.plist*
+
+Assembly-CSharp-Editor.csproj
+Assembly-CSharp.csproj

CONTRIBUTING.md

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+Want to contribute? Great! First, read this page (including the small print at the end).
+
+### Before you contribute
+Before we can use your code, you must sign the
+[Google Individual Contributor License Agreement](https://developers.google.com/open-source/cla/individual?csw=1)
+(CLA), which you can do online. The CLA is necessary mainly because you own the
+copyright to your changes, even after your contribution becomes part of our
+codebase, so we need your permission to use and distribute your code. We also
+need to be sure of various other things — for instance that you'll tell us if you
+know that your code infringes on other people's patents. You don't have to sign
+the CLA until after you've submitted your code for review and a member has
+approved it, but you must do it before we can put your code into our codebase.
+Before you start working on a larger contribution, you should get in touch with
+us first through the issue tracker with your idea so that we can help out and
+possibly guide you. Coordinating up front makes it much easier to avoid
+frustration later on.
+
+### Code reviews
+All submissions, including submissions by project members, require review. We
+use Github pull requests for this purpose.
+
+### The small print
+Contributions made by corporations are covered by a different agreement than
+the one above, the Software Grant and Corporate Contributor License Agreement.

GoogleSignInPlugin/Assets/GoogleSignIn.meta

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+// <copyright file="GoogleSignInDependencies.cs" company="Google Inc.">
+// Copyright (C) 2017 Google Inc. All Rights Reserved.
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//    limitations under the License.
+// </copyright>
+
+namespace GoogleSignIn.Editor {
+  using System;
+  using System.Collections.Generic;
+  using UnityEditor;
+  using UnityEngine;
+
+  /// <summary>
+  /// Google sign in dependencies.  This class registers the dependendies
+  /// on Google Play Services with the JarResolver plugin.
+  /// </summary>
+  [InitializeOnLoad]
+  public class GoogleSignInDependencies : AssetPostprocessor {
+
+    static GoogleSignInDependencies() {
+      AddDependencies();
+    }
+
+#if UNITY_ANDROID
+    public static object svcSupport;
+
+    static void AddDependencies() {
+      // Setup the resolver using reflection as the module may not be
+      // available at compile time.
+      Type playServicesSupport = Google.VersionHandler.FindClass(
+        "Google.JarResolver", "Google.JarResolver.PlayServicesSupport");
+      if (playServicesSupport == null) {
+        return;
+      }
+      svcSupport = svcSupport ?? Google.VersionHandler.InvokeStaticMethod(
+        playServicesSupport, "CreateInstance",
+        new object[] {"GoogleSignIn",
+                    EditorPrefs.GetString("AndroidSdkRoot"),
+                    "ProjectSettings"}
+      );
+      if (svcSupport != null) {
+        // The only direct dependency is on auth, min version 10.2.0.
+        Google.VersionHandler.InvokeInstanceMethod(svcSupport,
+                "DependOn", new object[] {
+                            "com.google.android.gms",
+                            "play-services-auth",
+                            "10.2+" },
+                    namedArgs: new Dictionary<string, object>() {
+                                {"packageIds", new string[] {
+                                    "extra-google-m2repository"
+                                    }
+                                }
+                    });
+      } else {
+        Debug.LogError("Jar resolver service not available.  " +
+          "Please add the Jar resolver to your project or ignore this error " +
+          " and manage the Google Play Services dependencies manually");
+      }
+    }
+#elif UNITY_IOS
+    static void AddDependencies() {
+            Type iosResolver = Google.VersionHandler.FindClass(
+      "Google.IOSResolver", "Google.IOSResolver");
+            if (iosResolver == null) {
+                return;
+            }
+
+            Google.VersionHandler.InvokeStaticMethod(
+          iosResolver, "AddPod",
+          new object[] { "GoogleSignIn" },
+          namedArgs: new Dictionary<string, object>() {
+          { "version", ">=  4.0.2" },
+          { "bitcodeEnabled", false },
+          });
+    }
+#endif  // UNITY_ANDROID / iOS
+  }
+}

GoogleSignInPlugin/Assets/GoogleSignIn/Editor.meta

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+// <copyright file="Future.cs" company="Google Inc.">
+// Copyright (C) 2017 Google Inc. All Rights Reserved.
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//    limitations under the License.
+// </copyright>
+namespace Google {
+  using System.Collections;
+  using System.Threading.Tasks;
+  using UnityEngine;
+
+  /// <summary>
+  /// Interface for implementations of the Future<T> API.
+  /// </summary>
+  internal interface FutureAPIImpl<T> {
+    bool Pending { get; }
+    GoogleSignInStatusCode Status { get; }
+    T Result { get; }
+  }
+
+  /// <summary>
+  /// Future return value.
+  /// </summary>
+  /// <remarks>This class provides a promise of a result from a method call.
+  /// The typical usage is to check the Pending property until it is false.
+  /// At this time either the Status or Result will be available for use.
+  /// Result is only set if  the operation was successful.
+  /// As a convience, a coroutine to complete a Task is provided.
+  /// </remarks>
+  public class Future<T> {
+
+    private FutureAPIImpl<T> apiImpl;
+
+    internal Future(FutureAPIImpl<T> impl) {
+      apiImpl = impl;
+    }
+
+    /// <summary>
+    /// Gets a value indicating whether this
+    /// <see cref="T:Google.Future`1"/> is pending.
+    /// </summary>
+    /// <value><c>true</c> if pending; otherwise, <c>false</c>.</value>
+    public bool Pending { get { return apiImpl.Pending; } }
+
+    /// <summary>
+    /// Gets the status.
+    /// </summary>
+    /// <value>The status is set when Pending == false.</value>
+    GoogleSignInStatusCode Status { get { return apiImpl.Status; } }
+
+    /// <summary>
+    /// Gets the result.
+    /// </summary>
+    /// <value>The result is set when Pending == false and there is no error.
+    /// </value>
+    T Result { get { return apiImpl.Result; } }
+
+    /// <summary>
+    /// Waits for result then completes the TaskCompleationSource.
+    /// </summary>
+    /// <returns>The for result.</returns>
+    /// <param name="tcs">Tcs.</param>
+    internal IEnumerator WaitForResult(TaskCompletionSource<T> tcs) {
+      yield return new WaitUntil(() => !Pending);
+      if (Status == GoogleSignInStatusCode.Canceled) {
+        tcs.SetCanceled();
+      } else if (Status == GoogleSignInStatusCode.Success ||
+            Status == GoogleSignInStatusCode.SuccessCached) {
+        tcs.SetResult(Result);
+      } else {
+        tcs.SetException(new GoogleSignIn.SignInException(Status));
+      }
+    }
+  }
+}