WebVR: flush before requesting sync token for mailbox

third_party/WebKit/Source/modules/vr/VRDisplay.cpp

Index: third_party/WebKit/Source/modules/vr/VRDisplay.cpp
diff --git a/third_party/WebKit/Source/modules/vr/VRDisplay.cpp b/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
index a98b7a8de59704317c8f0ffc8d6b0042e7a75bde..97eb96ef914cb21c49e865f167e633c22d4f53d8 100644
--- a/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
+++ b/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
@@ -611,12 +611,22 @@ void VRDisplay::submitFrame() {
 
   pending_previous_frame_render_ = true;
   pending_submit_frame_ = true;
-  display_->SubmitFrame(
-      vr_frame_id_,
-      gpu::MailboxHolder(static_image->GetMailbox(),
-                         static_image->GetSyncToken(), GL_TEXTURE_2D));
+
+  TRACE_EVENT_BEGIN0("gpu", "VRDisplay::GetMailbox");
+  auto mailbox = static_image->GetMailbox();
+  TRACE_EVENT_END0("gpu", "VRDisplay::GetMailbox");
+  // Flush to avoid black screen flashes which appear to be related to
+  // "fence sync must be flushed before generating sync token" GL errors.
+  context_gl_->Flush();
+  TRACE_EVENT_BEGIN0("gpu", "VRDisplay::GetSyncToken");
+  auto token = static_image->GetSyncToken();

[mthiesse, 2017/05/18 15:33:53]

s/token/sync_token

[klausw, 2017/05/18 17:47:39]

Done, this was a cherry-pick with a bad manual edit.

+  TRACE_EVENT_END0("gpu", "VRDisplay::GetSyncToken");
+  TRACE_EVENT_BEGIN0("gpu", "VRDisplay::SubmitFrame");
+  display_->SubmitFrame(vr_frame_id_,
+                        gpu::MailboxHolder(mailbox, sync_token, GL_TEXTURE_2D));
   did_submit_this_frame_ = true;
   RequestVSync();
+  TRACE_EVENT_END0("gpu", "VRDisplay::SubmitFrame");
 
   // If preserveDrawingBuffer is false, must clear now. Normally this
   // happens as part of compositing, but that's not active while