gpu: Ensure that preempted channels wake up after preemption.

content/common/gpu/gpu_channel.cc

Index: content/common/gpu/gpu_channel.cc
diff --git a/content/common/gpu/gpu_channel.cc b/content/common/gpu/gpu_channel.cc
index 127b1a1ff6054c97b2452fcbff75ea66655302f0..21ea23d89bcb5783e890d03985f924fa0e16525b 100644
--- a/content/common/gpu/gpu_channel.cc
+++ b/content/common/gpu/gpu_channel.cc
@@ -231,6 +231,10 @@ void GpuChannelMessageQueue::PauseMessageProcessing() {
   base::AutoLock auto_lock(channel_lock_);
   DCHECK(!channel_messages_.empty());
 
+  // If we have been preempted by another channel, just post a task to wake up.
+  if (scheduled_)
+    channel_->PostHandleMessage(this);
+
   sync_point_order_data_->PauseProcessingOrderNumber(
       channel_messages_.front()->order_number);
 }