Add support of vrdisplayconnect and vrdisplaydisconnect event

device/vr/android/gvr/gvr_device.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "device/vr/android/gvr/gvr_device.h"
 
 #include <math.h>
 #include <algorithm>
 
 #include "base/time/time.h"
 #include "base/trace_event/trace_event.h"
 #include "third_party/gvr-android-sdk/src/ndk-beta/include/vr/gvr/capi/include/gvr.h"
 #include "third_party/gvr-android-sdk/src/ndk-beta/include/vr/gvr/capi/include/gvr_types.h"
 #include "ui/gfx/transform.h"
 #include "ui/gfx/transform_util.h"
 
 namespace device {
 
 namespace {
 
 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() {}
 
 VRDisplayPtr GvrDevice::GetVRDevice() {
   TRACE_EVENT0("input", "GvrDevice::GetVRDevice");
 
   VRDisplayPtr device = VRDisplay::New();
 
   device->capabilities = VRDisplayCapabilities::New();
   device->capabilities->hasOrientation = true;
@@ skipping 89 matching lines @@
     pose->position[2] = decomposed_transform.translate[2];
   }
 
   return pose;
 }
 
 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