Implement WebVR presentation pausing for VR Shell Menu Mode

device/vr/android/gvr/gvr_device_provider.h

Index: device/vr/android/gvr/gvr_device_provider.h
diff --git a/device/vr/android/gvr/gvr_device_provider.h b/device/vr/android/gvr/gvr_device_provider.h
index 02f77583ffe40b6b46863e8073ab45194a29c8a0..a0f489e25077b7508178246c80503573953c79ed 100644
--- a/device/vr/android/gvr/gvr_device_provider.h
+++ b/device/vr/android/gvr/gvr_device_provider.h
@@ -22,20 +22,29 @@ class VRServiceImpl;
 class DEVICE_VR_EXPORT GvrDeviceProvider : public VRDeviceProvider {
  public:
   GvrDeviceProvider();
-  ~GvrDeviceProvider() override;
 
   void GetDevices(std::vector<VRDevice*>* devices) override;
   void Initialize() override;
 
-  // Called from GvrDevice
+  // Called from GvrDevice.
   bool RequestPresent();
   void ExitPresent();
 
-  // Called from GvrDelegate
+  // Called from GvrDelegate. May be called from any thread.
   void OnGvrDelegateReady(GvrDelegate* delegate);
   void OnGvrDelegateRemoved();
 
+  // May be called from any thread. This function is likely to be called from
+  // an arbitrary GL thread handling GVR controller updates.
+  void OnDisplayBlur();
+
+  // May be called from any thread. This function is likely to be called from
+  // an arbitrary GL thread handling GVR controller updates.
+  void OnDisplayFocus();
+
  private:
+  ~GvrDeviceProvider() override;
+
   void GvrDelegateReady(GvrDelegate* delegate);
   void GvrDelegateRemoved();