Support GPU VSync when DirectComposition isn't enabled

gpu/ipc/service/gpu_vsync_provider_win.cc

 // Copyright (c) 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 "gpu/ipc/service/gpu_vsync_provider_win.h"
 
 #include <string>
 
 #include "base/atomicops.h"
 #include "base/strings/stringprintf.h"
@@ skipping 172 matching lines @@
   monitor_info.cbSize = sizeof(MONITORINFOEX);
   BOOL success = GetMonitorInfo(monitor, &monitor_info);
   CHECK(success);
 
   if (current_device_name_.compare(monitor_info.szDevice) != 0) {
     // Monitor changed. Close the current adapter handle and open a new one.
     CloseAdapter();
     OpenAdapter(monitor_info.szDevice);
   }
 
-  if (WaitForVBlankEvent()) {
-    vsync_provider_->GetVSyncParameters(
-        base::Bind(&GpuVSyncWorker::SendVSyncUpdate, base::Unretained(this),
-                   base::TimeTicks::Now()));
-  }
+  // Crash if WaitForVBlankEvent fails to avoid spinning the loop.
+  CHECK(WaitForVBlankEvent());
+
+  vsync_provider_->GetVSyncParameters(
+      base::Bind(&GpuVSyncWorker::SendVSyncUpdate, base::Unretained(this),
+                 base::TimeTicks::Now()));
 
   Reschedule();
 }
 
 void GpuVSyncWorker::SendVSyncUpdate(base::TimeTicks now,
                                      base::TimeTicks timestamp,
                                      base::TimeDelta interval) {
   base::TimeDelta adjustment;
 
   if (!(timestamp.is_null() || interval.is_zero())) {
     // Timestamp comes from DwmGetCompositionTimingInfo and apparently it might
     // be up to 2-3 vsync cycles in the past or in the future.
     // The adjustment formula was suggested here:
     // http://www.vsynctester.com/firefoxisbroken.html
-    base::TimeDelta adjustment =
+    adjustment =
         ((now - timestamp + interval / 8) % interval + interval) % interval -
         interval / 8;
     timestamp = now - adjustment;
   } else {
     // DWM must be disabled.
     timestamp = now;
   }
 
   TRACE_EVENT1("gpu", "GpuVSyncWorker::SendVSyncUpdate", "adjustment",
                adjustment.ToInternalValue());
@@ skipping 161 matching lines @@
 void GpuVSyncProviderWin::OnVSync(base::TimeTicks timestamp,
                                   base::TimeDelta interval) {
   DCHECK(vsync_worker_->BelongsToWorkerThread());
 
   message_filter_->Send(
       base::MakeUnique<GpuCommandBufferMsg_UpdateVSyncParameters>(
           message_filter_->route_id(), timestamp, interval));
 }
 
 }  // namespace gpu