Implement lazy initialization for VrShellDelegate

chrome/android/java/src/org/chromium/chrome/browser/compositor/CompositorViewHolder.java

Index: chrome/android/java/src/org/chromium/chrome/browser/compositor/CompositorViewHolder.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/compositor/CompositorViewHolder.java b/chrome/android/java/src/org/chromium/chrome/browser/compositor/CompositorViewHolder.java
index 636e75bd94ba3827a7b3845647c69160660455ea..62a4933db2cd314a82d2699bb2de115f10a7d2f6 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/compositor/CompositorViewHolder.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/compositor/CompositorViewHolder.java
@@ -975,11 +975,12 @@ public class CompositorViewHolder extends FrameLayout
      * @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;
     }
 
@@ -989,6 +990,7 @@ public class CompositorViewHolder extends FrameLayout
      * @param tabModelSelector
      */
     public void onExitVR(TabModelSelector tabModelSelector) {
+        getSurfaceView().setVisibility(View.VISIBLE);
         attachToTabModelSelector(tabModelSelector);
     }