[Reland 2] Pepper takes ownership of a mailbox before passing it to the texture layer.

gpu/ipc/service/gpu_channel.cc

Index: gpu/ipc/service/gpu_channel.cc
diff --git a/gpu/ipc/service/gpu_channel.cc b/gpu/ipc/service/gpu_channel.cc
index c4014d1f6271facca4a037d94667a45f07aa522a..568e6be21bd474a2638e15221dbe86b3eef3c7e8 100644
--- a/gpu/ipc/service/gpu_channel.cc
+++ b/gpu/ipc/service/gpu_channel.cc
@@ -792,8 +792,10 @@ void GpuChannel::HandleMessage(
   HandleMessageHelper(msg);
 
   // If we get descheduled or yield while processing a message.
-  if (stub && stub->HasUnprocessedCommands()) {
-    DCHECK_EQ((uint32_t)GpuCommandBufferMsg_AsyncFlush::ID, msg.type());
+  if ((stub && stub->HasUnprocessedCommands()) ||
+      !message_queue->IsScheduled()) {
+    DCHECK((uint32_t)GpuCommandBufferMsg_AsyncFlush::ID == msg.type() ||
+           (uint32_t)GpuCommandBufferMsg_WaitSyncToken::ID == msg.type());
     message_queue->PauseMessageProcessing();
   } else {
     message_queue->FinishMessageProcessing();