Clean up WebVR RequestPresent and make callback asynchronous.

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 71358494c132b368391a79ce7c0c71228120f738..a9e940fbf1b2f3e3a89f31b1058c915e61fcb990 100644
--- a/device/vr/android/gvr/gvr_device.cc
+++ b/device/vr/android/gvr/gvr_device.cc
@@ -200,12 +200,14 @@ void GvrDevice::ResetPose() {
     gvr_api->RecenterTracking();
 }
 
-bool GvrDevice::RequestPresent(bool secure_origin) {
+void GvrDevice::RequestPresent(const base::Callback<void(bool)>& callback) {
+  gvr_provider_->RequestPresent(callback);
+}
+
+void GvrDevice::SetSecureOrigin(bool secure_origin) {
   secure_origin_ = secure_origin;
   if (delegate_)
     delegate_->SetWebVRSecureOrigin(secure_origin_);
-
-  return gvr_provider_->RequestPresent();
 }
 
 void GvrDevice::ExitPresent() {