Implement new compositor and ContentViewCore reparenting for VR Shell.

chrome/android/java/src/org/chromium/chrome/browser/tab/Tab.java

Index: chrome/android/java/src/org/chromium/chrome/browser/tab/Tab.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/tab/Tab.java b/chrome/android/java/src/org/chromium/chrome/browser/tab/Tab.java
index cd2483c6a21fab6f8fc74a00b6e3fb54a8f00278..7613c59f33a9636d75ce7c55056ce756724bdce6 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/tab/Tab.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/tab/Tab.java
@@ -1595,9 +1595,7 @@ public class Tab implements ViewGroup.OnHierarchyChangeListener,
         // TODO(yusufo): Share these calls with the construction related calls.
         // crbug.com/590281
 
-        // Update and propagate for the new WindowAndroid.
-        mWindowAndroid = activity.getWindowAndroid();
-        mContentViewCore.updateWindowAndroid(mWindowAndroid);
+        updateWindowAndroid(activity.getWindowAndroid());

[Ted C, 2016/09/20 19:57:06]

can we use this above in detach?  then we wouldn't need to change the content
layer, in your code, you could do updateWindowAndroid(null),
updateWindowAndroid(VrWindow).

I think longer term, we are going to want to break down detach and attach to
handle this case better where you could use more of this code.

If we do end up needing a separate activity, we'll want the ability to detach
the window w/o the related mutating the tab model/broadcasting an intent.

[mthiesse, 2016/09/20 20:56:07]

Acknowledged.

 
         // Update for the controllers that need the Compositor from the new Activity.
         attachTabContentManager(activity.getTabContentManager());
@@ -1627,6 +1625,15 @@ public class Tab implements ViewGroup.OnHierarchyChangeListener,
     }
 
     /**
+     * Update and propagate the new WindowAndroid.
+     * @param windowAndroid The WindowAndroid to propagate.
+     */
+    public void updateWindowAndroid(WindowAndroid windowAndroid) {
+        mWindowAndroid = windowAndroid;
+        mContentViewCore.updateWindowAndroid(mWindowAndroid);
+    }
+
+    /**
      * @return Whether the tab is detached from its Activity and {@link WindowAndroid} for
      * reparenting. Certain functionalities will not work until it is attached to a new activity
      * with {@link Tab#attachAndFinishReparenting(