Added a new example for google signin.

google_signin/lib/home.dart

@@ -0,0 +1,40 @@
+import 'package:flutter/material.dart';
+import 'package:meta/meta.dart';
+import 'package:flutter/foundation.dart';
+
+class Home extends StatelessWidget {
+  Home(
+      {Key key,
+      @required this.onSignin,
+      @required this.onLogout,
+      @required this.showLoading})
+      : super(key: key);
+
+  final VoidCallback onSignin;
+  final VoidCallback onLogout;
+  bool showLoading = false;
+
+  @override
+  Widget build(BuildContext context) {
+    return new Scaffold(
+      appBar: new AppBar(title: new Text("Sign In")),
+      body: new Container(
+          padding: const EdgeInsets.all(20.0),
+          child: new Center(
+            child: new Column(
+              mainAxisAlignment: MainAxisAlignment.center,
+              children: <Widget>[
+                showLoading
+                    ? new CircularProgressIndicator()
+                    : new RaisedButton(
+                        onPressed: this.onSignin,
+                        child: new Text("Sign In"),
+                        color: Colors.lightBlueAccent,
+                      ),
+                //new RaisedButton(onPressed: this.onLogout, child: new Text("Logout"), color: Colors.amberAccent),
+              ],
+            ),
+          )),
+    );
+  }
+}