Tentatively goes into WebVR presentation mode if page listens to vrdisplayactivate.

chrome/browser/android/vr_shell/vr_shell_delegate.h

Index: chrome/browser/android/vr_shell/vr_shell_delegate.h
diff --git a/chrome/browser/android/vr_shell/vr_shell_delegate.h b/chrome/browser/android/vr_shell/vr_shell_delegate.h
index fc09693f960fd89cedc7ef6e2a119f674d88a5d0..ba1937b649caba70e5ffd6314e0728683f9a3fec 100644
--- a/chrome/browser/android/vr_shell/vr_shell_delegate.h
+++ b/chrome/browser/android/vr_shell/vr_shell_delegate.h
@@ -68,6 +68,8 @@ class VrShellDelegate : public device::GvrDelegateProvider {
 
   void CreateNonPresentingDelegate();
 
+  void OnActivateDisplayHandled(bool present_requested);
+
   std::unique_ptr<NonPresentingGvrDelegate> non_presenting_delegate_;
   base::android::ScopedJavaGlobalRef<jobject> j_vr_shell_delegate_;
   device::GvrDeviceProvider* device_provider_ = nullptr;
@@ -78,6 +80,8 @@ class VrShellDelegate : public device::GvrDelegateProvider {
   device::mojom::VRSubmitFrameClientPtr submit_client_;
   bool pending_successful_present_request_ = false;
 
+  base::WeakPtrFactory<VrShellDelegate> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(VrShellDelegate);
 };