Implement lazy initialization for VrShellDelegate

chrome/android/java/src/org/chromium/chrome/browser/compositor/CompositorViewHolder.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.chrome.browser.compositor;
 
 import android.content.Context;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Paint;
@@ skipping 957 matching lines @@
         }
         mPendingInvalidations.clear();
     }
 
     /**
      * Detach and return the {@link TabModelSelector} in order to disconnect this
      * {@link CompositorViewHolder} so that VR can take ownership of Chrome's rendering.
      * @return The detached {@link TabModelSelector}.
      */
     public TabModelSelector detachForVR() {
-        mTabModelSelector.removeObserver(mTabModelSelectorObserver);
+        if (mTabModelSelector != null) mTabModelSelector.removeObserver(mTabModelSelectorObserver);
         TabModelSelector selector = mTabModelSelector;
         mTabModelSelector = null;
         mLayerTitleCache.setTabModelSelector(null);
         setTab(null);
+        getSurfaceView().setVisibility(View.INVISIBLE);
         return selector;
     }
 
     /**
      * Restores the {@link TabModelSelector} to this {@link CompositorViewHolder} after exiting VR
      * so that it can take back ownership of Chrome's rendering.
      * @param tabModelSelector
      */
     public void onExitVR(TabModelSelector tabModelSelector) {
+        getSurfaceView().setVisibility(View.VISIBLE);
         attachToTabModelSelector(tabModelSelector);
     }
 
     private void attachToTabModelSelector(TabModelSelector tabModelSelector) {
         assert mTabModelSelector == null;
         mTabModelSelector = tabModelSelector;
         mTabModelSelector.addObserver(mTabModelSelectorObserver);
 
         mLayerTitleCache.setTabModelSelector(mTabModelSelector);
         onContentChanged();
@@ skipping 125 matching lines @@
             if (mPixelRect.width() == 0) {
                 mPixelRect.right = mPixelRect.left + 1;
             }
             if (mPixelRect.height() == 0) {
                 mPixelRect.bottom = mPixelRect.top + 1;
             }
             return mPixelRect;
         }
     }
 }