Implement new compositor and ContentViewCore reparenting for VR Shell.

chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java

Index: chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
index 8aa2998dbf3809c555907c3be86973c650da505d..113164f88a51c1a131a872f8513836d466a065be 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
@@ -15,6 +15,7 @@ import android.view.WindowManager;
 
 import org.chromium.base.Log;
 import org.chromium.chrome.browser.ChromeTabbedActivity;
+import org.chromium.chrome.browser.tab.Tab;
 
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
@@ -71,6 +72,12 @@ public class VrShellDelegate {
      */
     public boolean enterVRIfNecessary() {
         if (!mVrShellEnabled) return false;
+        Tab tab = mActivity.getActivityTab();

[bshe, 2016/09/12 16:39:56]

Did you try cold start browser? The active tab might not be ready when you call
this function.

[mthiesse, 2016/09/12 21:46:04]

Cold start of the browser works just fine for entering VR - it's just not pretty
at the moment.

Even if the tab isn't ready yet that's fine for now - we just won't enter VR.

+        // TODO(mthiesse): When we have VR UI for opening new tabs, etc., allow VR Shell to be
+        // entered without any current tabs.
+        if (tab == null || tab.getContentViewCore() == null) {
+            return false;
+        }
         if (mInVr) return true;
         mActivity.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
         if (!createVrShell()) {
@@ -79,7 +86,7 @@ public class VrShellDelegate {
         }
         addVrViews();
         setupVrModeWindowFlags();
-        mVrShellView.onNativeLibraryReady();
+        mVrShellView.onNativeLibraryReady(tab.getContentViewCore());
         mVrShellView.setVrModeEnabled(true);
         mInVr = true;
         return true;