Add android.mojo application.

shell/android/apk/src/org/chromium/mojo/shell/ViewportActivity.java

Index: shell/android/apk/src/org/chromium/mojo/shell/ViewportActivity.java
diff --git a/shell/android/apk/src/org/chromium/mojo/shell/ViewportActivity.java b/shell/android/apk/src/org/chromium/mojo/shell/ViewportActivity.java
index 29b69a7b5bc785a175f5278bed0f6f03b5ea7098..b087cd0e37809becbf524e0b379924c5a7ac68df 100644
--- a/shell/android/apk/src/org/chromium/mojo/shell/ViewportActivity.java
+++ b/shell/android/apk/src/org/chromium/mojo/shell/ViewportActivity.java
@@ -19,6 +19,12 @@ import org.chromium.mojo.input.InputServiceImpl;
  * Activity for displaying on the screen from the NativeViewportService.
  */
 public class ViewportActivity extends Activity {
+    private static Activity sCurrentActivity = null;
+
+    public static Activity getCurrent() {
+        return sCurrentActivity;
+    }
+
     /**
      * @see Activity#onKeyDown(int, KeyEvent)
      */
@@ -57,4 +63,22 @@ public class ViewportActivity extends Activity {
         super.onNewIntent(intent);
         new RuntimeException("This activity instance should only ever receive one intent.");
     }
+
+    /**
+     * @see Activity#onPause()
+     */
+    @Override
+    protected void onPause() {
+        if (sCurrentActivity == this) sCurrentActivity = null;
+        super.onPause();
+    }
+
+    /**
+     * @see Activity#onResume()
+     */
+    @Override
+    protected void onResume() {
+        super.onResume();
+        sCurrentActivity = this;
+    }
 }