Allow AllocateGpuMemoryBuffer to be called from multiple threads.

content/browser/renderer_host/render_message_filter.cc

Index: content/browser/renderer_host/render_message_filter.cc
diff --git a/content/browser/renderer_host/render_message_filter.cc b/content/browser/renderer_host/render_message_filter.cc
index 55e10b5cf34afc9fd5ceddb9fb8637cf7d899be2..29c39c43441495fb5fa9f509271fb57251653a80 100644
--- a/content/browser/renderer_host/render_message_filter.cc
+++ b/content/browser/renderer_host/render_message_filter.cc
@@ -376,6 +376,15 @@ void RenderMessageFilter::OnChannelConnected(int32 peer_id) {
 
 bool RenderMessageFilter::OnMessageReceived(const IPC::Message& message,
                                             bool* message_was_ok) {
+#if defined(OS_MACOSX)
+  // Remove surface references that are now in use by the renderer.
+  while (!io_surfaces_.empty()) {
+    IOSurfaceSupport* io_surface_support = IOSurfaceSupport::Initialize();
+    if (!io_surface_support->IOSurfaceIsInUse(io_surfaces_.front()))
+      break;
+    io_surfaces_.pop();
+  }
+#endif
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP_EX(RenderMessageFilter, message, *message_was_ok)
 #if defined(OS_WIN)
@@ -1220,10 +1229,9 @@ void RenderMessageFilter::OnAllocateGpuMemoryBuffer(
         handle->type = gfx::IO_SURFACE_BUFFER;
         handle->io_surface_id = io_surface_support->IOSurfaceGetID(io_surface);
 
-        // TODO(reveman): This makes the assumption that the renderer will
-        // grab a reference to the surface before sending another message.
-        // crbug.com/325045
-        last_io_surface_ = io_surface;
+        DCHECK(!io_surface_support->IOSurfaceIsInUse(io_surface));
+        // Keep a reference to the surface until it's in use by the renderer.
+        io_surfaces_.push(io_surface);
         return;
       }
     }