Allow native_viewport to create new native windows on demand on Android.

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

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.mojo.shell;
+
+import android.app.Activity;
+import android.app.UiModeManager;
+import android.content.Intent;
+import android.content.res.Configuration;
+import android.os.Bundle;
+import android.view.WindowManager;
+
+import org.chromium.mojo.PlatformViewportAndroid;
+
+/**
+ * Activity for displaying on the screen from the NativeViewportService.
+ */
+public class ViewportActivity extends Activity {
+    private static final String TAG = "ViewportActivity";
+    private PlatformViewportAndroid mPlatformViewport;
+
+    @Override
+    protected void onCreate(final Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+
+        if (!PlatformViewportAndroid.newActivityStarted(this)) {
+            // We have not attached to a viewport, so there's no point continuing.
+            finishAndRemoveTask();
+        }
+
+        // TODO(tonyg): Watch activities go back to the home screen within a
+        // couple of seconds of detaching from adb. So for demonstration purposes,
+        // we just keep the screen on. Eventually we'll want a solution for
+        // allowing the screen to sleep without quitting the shell.
+        // TODO(etiennej): Verify the above is still true after the switch to a Service model.
+        UiModeManager uiModeManager = (UiModeManager) getSystemService(UI_MODE_SERVICE);
+        if (uiModeManager.getCurrentModeType() == Configuration.UI_MODE_TYPE_WATCH) {
+            getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
+        }
+    }
+
+    @Override
+    public void onNewIntent(Intent intent) {
+        super.onNewIntent(intent);
+        new RuntimeException("This activity instance should only ever receive one intent.");
+    }
+}