Refactor GvrDelegate ownership into GvrDelegateProvider and fix more threading violations.

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 8f0b7f14d173c079f5690ecdca833af864497d2c..94723aa9bb59ca50119f1d2a09dc6a17f480fe46 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
@@ -414,9 +414,6 @@ public class VrShellDelegate {
             mRequestedWebVR = false;
         }
 
-        // TODO(bshe): Ideally, we do not need two gvr context exist at the same time. We can
-        // probably shutdown non presenting gvr when presenting and create a new one after exit
-        // presenting. See crbug.com/655242
         StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskWrites();
         try {
             nativeOnResume(mNativeVrShellDelegate);