Added a new example for google signin.

Author: Hariharan

google_signin/.gitignore

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+.DS_Store
+.atom/
+.idea
+.vscode/
+.packages
+.pub/
+build/
+ios/.generated/
+packages
+.flutter-plugins

google_signin/README.md

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+# google_signin
+
+A simple flutter app to demonstrate Google signin using Firebase. Register your app on Firebase and enable Google authentication.
+
+![Initial Page](page1.jpg)
+![Login Dialog](page2.jpg)
+![User Page](page3.jpg)
+
+## Getting Started
+
+For help getting started with Flutter, view our online
+[documentation](https://flutter.io/).

google_signin/android/.gitignore

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+*.iml
+*.class
+.gradle
+/local.properties
+/.idea/workspace.xml
+/.idea/libraries
+.DS_Store
+/build
+/captures
+GeneratedPluginRegistrant.java

google_signin/android/app/build.gradle

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+def localProperties = new Properties()
+def localPropertiesFile = rootProject.file('local.properties')
+if (localPropertiesFile.exists()) {
+    localPropertiesFile.withReader('UTF-8') { reader ->
+        localProperties.load(reader)
+    }
+}
+
+def flutterRoot = localProperties.getProperty('flutter.sdk')
+if (flutterRoot == null) {
+    throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file.")
+}
+
+apply plugin: 'com.android.application'
+apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
+
+android {
+    compileSdkVersion 27
+
+    lintOptions {
+        disable 'InvalidPackage'
+    }
+
+    defaultConfig {
+        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
+        applicationId "com.theroboticlab.googlesignin"
+        minSdkVersion 16
+        targetSdkVersion 27
+        versionCode 1
+        versionName "1.0"
+        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
+    }
+
+    buildTypes {
+        release {
+            // TODO: Add your own signing config for the release build.
+            // Signing with the debug keys for now, so `flutter run --release` works.
+            signingConfig signingConfigs.debug
+        }
+    }
+}
+
+flutter {
+    source '../..'
+}
+
+dependencies {
+    testImplementation 'junit:junit:4.12'
+    androidTestImplementation 'com.android.support.test:runner:1.0.1'
+    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
+    implementation 'com.firebaseui:firebase-ui-auth:4.0.0'
+
+}
+apply plugin: 'com.google.gms.google-services'

google_signin/android/app/src/main/AndroidManifest.xml

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+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="com.theroboticlab.googlesignin">
+
+    <!-- The INTERNET permission is required for development. Specifically,
+         flutter needs it to communicate with the running application
+         to allow setting breakpoints, to provide hot reload, etc.
+    -->
+    <uses-permission android:name="android.permission.INTERNET"/>
+
+    <!-- io.flutter.app.FlutterApplication is an android.app.Application that
+         calls FlutterMain.startInitialization(this); in its onCreate method.
+         In most cases you can leave this as-is, but you if you want to provide
+         additional functionality it is fine to subclass or reimplement
+         FlutterApplication and put your custom class here. -->
+    <application
+        android:name="io.flutter.app.FlutterApplication"
+        android:label="google_signin"
+        android:icon="@mipmap/ic_launcher">
+        <activity
+            android:name=".MainActivity"
+            android:launchMode="singleTop"
+            android:theme="@style/LaunchTheme"
+            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale"
+            android:hardwareAccelerated="true"
+            android:windowSoftInputMode="adjustResize">
+            <!-- This keeps the window background of the activity showing
+                 until Flutter renders its first frame. It can be removed if
+                 there is no splash screen (such as the default splash screen
+                 defined in @style/LaunchTheme). -->
+            <meta-data
+                android:name="io.flutter.app.android.SplashScreenUntilFirstFrame"
+                android:value="true" />
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN"/>
+                <category android:name="android.intent.category.LAUNCHER"/>
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>

google_signin/android/app/src/main/java/com/theroboticlab/googlesignin/MainActivity.java

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+package com.theroboticlab.googlesignin;
+
+import android.os.Bundle;
+
+import io.flutter.app.FlutterActivity;
+import io.flutter.plugins.GeneratedPluginRegistrant;
+
+public class MainActivity extends FlutterActivity {
+  @Override
+  protected void onCreate(Bundle savedInstanceState) {
+    super.onCreate(savedInstanceState);
+    GeneratedPluginRegistrant.registerWith(this);
+  }
+}

google_signin/android/app/src/main/res/drawable/launch_background.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<!-- Modify this file to customize your launch splash screen -->
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="@android:color/white" />
+
+    <!-- You can insert your own image assets here -->
+    <!-- <item>
+        <bitmap
+            android:gravity="center"
+            android:src="@mipmap/launch_image" />
+    </item> -->
+</layer-list>