Update /examples/ to new gradle based build flow (#8173)

* Update hello_world to new gradle based build flow

* Update flutter_gallery to gradle based build

* Align hello_services with new gradle based build

* Update platform_services to new gradle based build

* Upgrade stock to gradle based build
diff --git a/examples/stocks/android/app/build.gradle b/examples/stocks/android/app/build.gradle
new file mode 100644
index 0000000..90c2899
--- /dev/null
+++ b/examples/stocks/android/app/build.gradle
@@ -0,0 +1,46 @@
+def localProperties = new Properties()
+def localPropertiesFile = rootProject.file('local.properties')
+if (localPropertiesFile.exists()) {
+    localPropertiesFile.withInputStream { stream ->
+        localProperties.load(stream)
+    }
+}
+
+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 25
+    buildToolsVersion '24.0.1'
+
+    lintOptions {
+        disable 'InvalidPackage'
+    }
+
+    defaultConfig {
+        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 {
+    androidTestCompile 'com.android.support:support-annotations:25.0.0'
+    androidTestCompile 'com.android.support.test:runner:0.5'
+    androidTestCompile 'com.android.support.test:rules:0.5'
+}