Add support of vrdisplayconnect and vrdisplaydisconnect event

device/vr/android/gvr/gvr_device.h

Index: device/vr/android/gvr/gvr_device.h
diff --git a/device/vr/android/gvr/gvr_device.h b/device/vr/android/gvr/gvr_device.h
index 83745312834cb467eba2e295bf1afd7a9ebeedfc..4571ab16ead61219dcc5e085b109fbf07d146a56 100644
--- a/device/vr/android/gvr/gvr_device.h
+++ b/device/vr/android/gvr/gvr_device.h
@@ -24,9 +24,13 @@ class GvrDevice : public VRDevice {
   VRPosePtr GetPose() override;
   void ResetPose() override;
 
+  virtual void PollEvents() override;
+
  private:
   gvr::GvrApi* gvr_api_;
 
+  bool isConnected;
+
   DISALLOW_COPY_AND_ASSIGN(GvrDevice);
 };