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

chrome/browser/android/vr_shell/vr_shell_gl.cc

Index: chrome/browser/android/vr_shell/vr_shell_gl.cc
diff --git a/chrome/browser/android/vr_shell/vr_shell_gl.cc b/chrome/browser/android/vr_shell/vr_shell_gl.cc
index 73afb7117c0ac2266959055deaf971b4f109f303..715b354a182d8105ab013bc6650304728212af74 100644
--- a/chrome/browser/android/vr_shell/vr_shell_gl.cc
+++ b/chrome/browser/android/vr_shell/vr_shell_gl.cc
@@ -175,7 +175,13 @@ VrShellGl::VrShellGl(
 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(
@@ -1091,6 +1097,8 @@ void VrShellGl::OnRequest(device::mojom::VRVSyncProviderRequest 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;
@@ -1135,7 +1143,8 @@ void VrShellGl::SendVSync(base::TimeDelta time,
 
   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() {