Prevent browser crash resulting from misbehaving WebVR renderer requesting multiple VSyncs.

chrome/browser/android/vr_shell/vr_shell_gl.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 "chrome/browser/android/vr_shell/vr_shell_gl.h"
 
 #include <limits>
 #include <utility>
 
 #include "base/android/jni_android.h"
@@ skipping 157 matching lines @@
         weak_vr_shell_(weak_vr_shell),
         delegate_provider_(delegate_provider),
         main_thread_task_runner_(std::move(main_thread_task_runner)),
         weak_ptr_factory_(this) {
   GvrInit(gvr_api);
 }
 
 VrShellGl::~VrShellGl() {
   vsync_task_.Cancel();
   if (!callback_.is_null()) {
-    base::ResetAndReturn(&callback_).Run(nullptr, base::TimeDelta(), -1);
+    // When this VSync provider is going away we have to respond to pending
+    // callbacks, so instead of providing a VSync, tell the requester to try
+    // again. A VSyncProvider is guaranteed to exist, so the request in response
+    // to this message will go through some other VSyncProvider.
+    base::ResetAndReturn(&callback_)
+        .Run(nullptr, base::TimeDelta(), -1,
+             device::mojom::VRVSyncProvider::Error::ERROR_TRY_AGAIN);
   }
   if (binding_.is_bound()) {
     main_thread_task_runner_->PostTask(FROM_HERE, base::Bind(
         &VrShellDelegate::OnVRVsyncProviderRequest, delegate_provider_,
         base::Passed(binding_.Unbind())));
   }
 }
 
 void VrShellGl::Initialize() {
   scene_.reset(new UiScene);
@@ skipping 895 matching lines @@
 }
 
 void VrShellGl::OnRequest(device::mojom::VRVSyncProviderRequest request) {
   binding_.Close();
   binding_.Bind(std::move(request));
 }
 
 void VrShellGl::GetVSync(const GetVSyncCallback& callback) {
   if (!pending_vsync_) {
     if (!callback_.is_null()) {
+      callback.Run(nullptr, base::TimeDelta(), -1,
+                   device::mojom::VRVSyncProvider::Error::ERROR_BAD_REQUEST);
       mojo::ReportBadMessage("Requested VSync before waiting for response to "
           "previous request.");
       return;
     }
     callback_ = callback;
     return;
   }
   pending_vsync_ = false;
   SendVSync(pending_time_, callback);
 }
@@ skipping 24 matching lines @@
 
   gvr::ClockTimePoint target_time = gvr::GvrApi::GetTimePointNow();
   target_time.monotonic_system_time_nanos += kPredictionTimeWithoutVsyncNanos;
 
   gvr::Mat4f head_mat =
       gvr_api_->GetHeadSpaceFromStartSpaceRotation(target_time);
   head_mat = gvr_api_->ApplyNeckModel(head_mat, 1.0f);
 
   webvr_head_pose_[frame_index % kPoseRingBufferSize] = head_mat;
 
-  callback.Run(VrShell::VRPosePtrFromGvrPose(head_mat), time, frame_index);
+  callback.Run(VrShell::VRPosePtrFromGvrPose(head_mat), time, frame_index,
+               device::mojom::VRVSyncProvider::Error::ERROR_NONE);
 }
 
 void VrShellGl::ResetPose() {
   // Should never call RecenterTracking when using with Daydream viewers. On
   // those devices recentering should only be done via the controller.
   if (gvr_api_ && gvr_api_->GetViewerType() == GVR_VIEWER_TYPE_CARDBOARD)
     gvr_api_->RecenterTracking();
 }
 
 void VrShellGl::CreateVRDisplayInfo(
     const base::Callback<void(device::mojom::VRDisplayInfoPtr)>& callback,
     uint32_t device_id) {
   device::mojom::VRDisplayInfoPtr info = VrShell::CreateVRDisplayInfo(
       gvr_api_.get(), content_tex_physical_size_, device_id);
   main_thread_task_runner_->PostTask(
       FROM_HERE,
       base::Bind(&RunVRDisplayInfoCallback, callback, base::Passed(&info)));
 }
 
 }  // namespace vr_shell