Renderer reading side of gamepad

content/browser/gamepad/gamepad_provider.cc

Index: content/browser/gamepad/gamepad_provider.cc
diff --git a/content/browser/gamepad/gamepad_provider.cc b/content/browser/gamepad/gamepad_provider.cc
index 642e2445a7bbe8fa0d0fc8fa7fd1fcbe2827c101..06b2165a125385304bfd845f4af3562f7ff1daf5 100644
--- a/content/browser/gamepad/gamepad_provider.cc
+++ b/content/browser/gamepad/gamepad_provider.cc
@@ -119,9 +119,17 @@ void Provider::DoInitializePollingThread() {
 void Provider::DoPoll() {
   DCHECK(MessageLoop::current() == polling_thread_->message_loop());
   GamepadHardwareBuffer* hwbuf = SharedMemoryAsHardwareBuffer();
-  base::subtle::Barrier_AtomicIncrement(&hwbuf->start_marker, 1);
+
+  ANNOTATE_BENIGN_RACE_SIZED(
+      &hwbuf->buffer,
+      sizeof(WebKit::WebGamepads),
+      "Racey reads are discarded");
+
+  // Acquire the SeqLock. There is only ever one writer to this data.
+  // See gamepad_hardware_buffer.h.
+  hwbuf->sequence.WriteBegin();
   data_fetcher_->GetGamepadData(&hwbuf->buffer, devices_changed_);
-  base::subtle::Barrier_AtomicIncrement(&hwbuf->end_marker, 1);
+  hwbuf->sequence.WriteEnd();
   devices_changed_ = false;
   // Schedule our next interval of polling.
   ScheduleDoPoll();