Fix Mac resize, delete more Mac code

gpu/ipc/client/gpu_channel_host.cc

Index: gpu/ipc/client/gpu_channel_host.cc
diff --git a/gpu/ipc/client/gpu_channel_host.cc b/gpu/ipc/client/gpu_channel_host.cc
index be6a3f79d6c16c9d500f10e50735ad7694d09a6a..7fa0b92f9dc345cb84b9371f6d9e034df8479f41 100644
--- a/gpu/ipc/client/gpu_channel_host.cc
+++ b/gpu/ipc/client/gpu_channel_host.cc
@@ -24,6 +24,10 @@
 #include "ipc/ipc_sync_message_filter.h"
 #include "url/gurl.h"
 
+#if defined(OS_MACOSX)
+#include "ui/accelerated_widget_mac/window_resize_helper_mac.h"
+#endif
+
 using base::AutoLock;
 
 namespace gpu {
@@ -446,7 +450,15 @@ bool GpuChannelHost::MessageFilter::OnMessageReceived(
     return false;
 
   const ListenerInfo& info = it->second;
-  info.task_runner->PostTask(
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner = info.task_runner;
+#if defined(OS_MACOSX)
+  // On Mac, the IPCs ViewHostMsg_SwapCompositorFrame, ViewHostMsg_UpdateRect,
+  // and GpuCommandBufferMsg_SwapBuffersCompleted need to be handled in a
+  // nested message loop during resize.
+  if (message.type() == GpuCommandBufferMsg_SwapBuffersCompleted::ID)
+    task_runner = ui::WindowResizeHelperMac::Get()->task_runner();

[piman, 2016/05/10 22:24:16]

This is called in the renderer - e.g. for pepper. Does this make sense there?
Should we inject the task runner instead when creating the UI context, to avoid
this extra odd dependency?

[ccameron, 2016/05/11 06:23:01]

Good point -- moved the #if MAC parts into
GpuProcessTransportFactory::EstablishedGpuChannel (which has lots of OS-specific
goo).

+#endif
+  task_runner->PostTask(
       FROM_HERE,
       base::Bind(base::IgnoreResult(&IPC::Listener::OnMessageReceived),
                  info.listener, message));