Add support of vrdisplayconnect and vrdisplaydisconnect event

device/vr/android/gvr/gvr_device.cc

Index: device/vr/android/gvr/gvr_device.cc
diff --git a/device/vr/android/gvr/gvr_device.cc b/device/vr/android/gvr/gvr_device.cc
index 2de6b12f0c8de234f8cee89354b35d8e0b0028d3..2357e785da9b9dd90670c6d582cf12bf669ee210 100644
--- a/device/vr/android/gvr/gvr_device.cc
+++ b/device/vr/android/gvr/gvr_device.cc
@@ -23,7 +23,9 @@ static const uint64_t kPredictionTimeWithoutVsyncNanos = 50000000;
 }  // namespace
 
 GvrDevice::GvrDevice(VRDeviceProvider* provider, gvr::GvrApi* gvr_api)
-    : VRDevice(provider), gvr_api_(gvr_api) {}
+    : VRDevice(provider), gvr_api_(gvr_api) {
+  isConnected = false;
+}
 
 GvrDevice::~GvrDevice() {}
 
@@ -133,4 +135,22 @@ void GvrDevice::ResetPose() {
   gvr_api_->ResetTracking();
 }
 
+// There are two conditions which hint that connection status has been changed.
+// First, if the GvrApi pointer is valid and nativeContext could be acquired,
+// the

[mthiesse, 2016/09/06 23:39:24]

nit: fix comment formatting.

+// connection may be built.
+// Second, if the GvrApi pointer is invalid or nativeContext couldn't be
+// acquired, the
+// connection may be lost.
+void GvrDevice::PollEvents() {

[bajones, 2016/09/06 23:57:26]

Sorry, I'm also realizing that this is a signal that is probably better handled
in GvrDeviceProvider::OnGvrApiInitialized and
GvrDeviceProvider::OnGvrApiShutdown (which will be renamed once
https://codereview.chromium.org/2309523003/ lands.) Those two functions should
act as very clear connected/disconnected signals for the purposes of GVR, making
a polling loop unnecessary.

[shaobo.yan, 2016/09/07 00:49:19]

Hi, brandon, thx for reviewing! I agree that OnGvrApiInitialized and
OnGvrApiShutdown is the place to handle connected/disconnected signals. But What
I concerned is how about the situation of reconnection? if we handle connected
signal in OnGvrApiInitialized, does it means that every time reconnection
happened, an old device object will be discarded and a new device object will be
created?

+  if (!client())
+    return;
+
+  if ((!isConnected && gvr_api_ && gvr_api_->GetContext()) ||
+      (isConnected && (!gvr_api_ || (gvr_api_ && !gvr_api_->GetContext())))) {
+    isConnected = !isConnected;
+    client()->OnDeviceConnectionStatusChanged(this, isConnected);
+  }
+}
+
 }  // namespace device