Re-land: Mark async texture uploads as completed from the upload thread.

content/common/gpu/gpu_command_buffer_stub.cc

Index: content/common/gpu/gpu_command_buffer_stub.cc
diff --git a/content/common/gpu/gpu_command_buffer_stub.cc b/content/common/gpu/gpu_command_buffer_stub.cc
index de8d19683f4d56911f871f5e96b453933dd87095..c0cf2150bcdd69d23d04b73376b6682ec6abcc49 100644
--- a/content/common/gpu/gpu_command_buffer_stub.cc
+++ b/content/common/gpu/gpu_command_buffer_stub.cc
@@ -299,6 +299,9 @@ void GpuCommandBufferStub::Destroy() {
   while (!sync_points_.empty())
     OnRetireSyncPoint(sync_points_.front());
 
+  if (decoder_.get())
+    decoder_->set_engine(NULL);
+
   // The scheduler has raw references to the decoder and the command buffer so
   // destroy it before those.
   scheduler_.reset();