Teach SkyShell.apk to stop posting frames when not visible

sky/shell/android/org/domokit/sky/shell/PlatformViewAndroid.java

Index: sky/shell/android/org/domokit/sky/shell/PlatformViewAndroid.java
diff --git a/sky/shell/android/org/domokit/sky/shell/PlatformViewAndroid.java b/sky/shell/android/org/domokit/sky/shell/PlatformViewAndroid.java
index aa807efee02286efb2597d8ee3594d295da49cbd..be7dbf41d6bebdaf0c4785824ccc3c0bef9a12b5 100644
--- a/sky/shell/android/org/domokit/sky/shell/PlatformViewAndroid.java
+++ b/sky/shell/android/org/domokit/sky/shell/PlatformViewAndroid.java
@@ -97,6 +97,10 @@ public class PlatformViewAndroid extends SurfaceView
         KeyboardServiceImpl.setActiveView(this);
     }
 
+    SkyEngine getEngine() {
+        return mSkyEngine;
+    }
+
     @Override
     protected void onDetachedFromWindow() {
         getHolder().removeCallback(mSurfaceCallback);
@@ -199,24 +203,6 @@ public class PlatformViewAndroid extends SurfaceView
         mSkyEngine.onInputEvent(event);
     }
 
-    public void onBackPressed() {
-        InputEvent event = new InputEvent();
-        event.type = EventType.BACK;
-        mSkyEngine.onInputEvent(event);
-    }
-
-    public void loadSnapshot(String path) {
-        mSkyEngine.runFromSnapshot(path);
-    }
-
-    public void loadBundle(String path) {
-        mSkyEngine.runFromBundle(path);
-    }
-
-    public void loadUrl(String url) {
-        mSkyEngine.runFromNetwork(url);
-    }
-
     private void attach() {
         Core core = CoreImpl.getInstance();
         Pair<SkyEngine.Proxy, InterfaceRequest<SkyEngine>> result =