Add an icon for SkyDemo (required by the play store)

R=abarth@chromium.org, eseidel@chromium.org

Review URL: https://codereview.chromium.org/1018033002

apk/demo/AndroidManifest.xml

@@ -10,7 +10,7 @@
     <uses-permission android:name="android.permission.INTERNET"/>
     <uses-feature android:name="android.hardware.sensor.accelerometer" android:required="true" />
 
-    <application android:name="SkyDemoApplication" android:label="Sky">
+    <application android:icon="@mipmap/ic_launcher" android:name="SkyDemoApplication" android:label="Sky">
         <activity android:name="SkyDemoActivity"
                   android:launchMode="singleTask"
                   android:theme="@android:style/Theme.Holo.Light.NoActionBar"

apk/demo/BUILD.gn

@@ -31,5 +31,11 @@ sky_apk("demo") {
   android_manifest = "AndroidManifest.xml"
   deps = [
     ":java",
+    ":demo_resources",
   ]
 }
+
+android_resources("demo_resources") {
+  resource_dirs = [ "res" ]
+  android_manifest = "AndroidManifest.xml"
+}