Move Mailbox from cc to gpu, and its traits to gpu/ipc

content/renderer/gpu/mailbox_output_surface.h

Index: content/renderer/gpu/mailbox_output_surface.h
diff --git a/content/renderer/gpu/mailbox_output_surface.h b/content/renderer/gpu/mailbox_output_surface.h
index 0f5336abc8573d55596113d64222c824e635e4ce..745a81257a8fa966a6ef91e6a75245976f720133 100644
--- a/content/renderer/gpu/mailbox_output_surface.h
+++ b/content/renderer/gpu/mailbox_output_surface.h
@@ -47,14 +47,14 @@ class MailboxOutputSurface : public CompositorOutputSurface {
         : texture_id(0) {}
 
     TransferableFrame(uint32 texture_id,
-                      const cc::Mailbox& mailbox,
+                      const gpu::Mailbox& mailbox,
                       const gfx::Size size)
         : texture_id(texture_id),
           mailbox(mailbox),
           size(size) {}
 
     uint32 texture_id;
-    cc::Mailbox mailbox;
+    gpu::Mailbox mailbox;
     gfx::Size size;
   };
   TransferableFrame current_backing_;