cc: Add GpuMemoryBufferHandle to TextureMailbox

content/common/cc_messages.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // IPC Messages sent between compositor instances.
 
 #include "cc/output/begin_frame_args.h"
 #include "cc/output/compositor_frame.h"
 #include "cc/output/compositor_frame_ack.h"
 #include "cc/output/filter_operation.h"
@@ skipping 264 matching lines @@
 IPC_STRUCT_TRAITS_END()
 
 IPC_STRUCT_TRAITS_BEGIN(cc::TransferableResource)
   IPC_STRUCT_TRAITS_MEMBER(id)
   IPC_STRUCT_TRAITS_MEMBER(format)
   IPC_STRUCT_TRAITS_MEMBER(filter)
   IPC_STRUCT_TRAITS_MEMBER(size)
   IPC_STRUCT_TRAITS_MEMBER(mailbox_holder)
   IPC_STRUCT_TRAITS_MEMBER(read_lock_fences_enabled)
   IPC_STRUCT_TRAITS_MEMBER(is_software)
+  IPC_STRUCT_TRAITS_MEMBER(gpu_memory_buffer_handle)

[piman, 2016/05/03 23:40:49]

drive-by: 3 concerns here:
1- this means the browser has to trust handles coming from the renderer, this
seems dangerous? The renderer already asked the browser to create that handle,
so the browser should already knows about it, is there a way to refer to it
other than by handle?
2- when receiving the message on the browser side, it creates a new handle
there, which needs to be closed by someone - including in early outs of
RenderWidgetHostImpl::OnSwapCompositorFrame.
3- on the sender side, there is a potential for a race if the GMB is destroyed
on the compositor thread (or other thread) before the IO thread had a chance to
send the message (which is async, so you don't know when that happens) - Very
Bad Things happen in that case (potential for random handle to be sent and/or
closed instead). The typical pattern is to duplicate the handle and have the IPC
system close that after sending (see FileDescriptor::auto_close or
SharedMemoryHandle::OwnershipPassesToIPC())

   IPC_STRUCT_TRAITS_MEMBER(is_overlay_candidate)
 IPC_STRUCT_TRAITS_END()
 
 IPC_STRUCT_TRAITS_BEGIN(cc::ReturnedResource)
   IPC_STRUCT_TRAITS_MEMBER(id)
   IPC_STRUCT_TRAITS_MEMBER(sync_token)
   IPC_STRUCT_TRAITS_MEMBER(count)
   IPC_STRUCT_TRAITS_MEMBER(lost)
 IPC_STRUCT_TRAITS_END()
 
@@ skipping 40 matching lines @@
   IPC_STRUCT_TRAITS_MEMBER(satisfies_sequences)
   IPC_STRUCT_TRAITS_MEMBER(referenced_surfaces)
 IPC_STRUCT_TRAITS_END()
 
 IPC_STRUCT_TRAITS_BEGIN(cc::GLFrameData)
   IPC_STRUCT_TRAITS_MEMBER(mailbox)
   IPC_STRUCT_TRAITS_MEMBER(sync_token)
   IPC_STRUCT_TRAITS_MEMBER(size)
   IPC_STRUCT_TRAITS_MEMBER(sub_buffer_rect)
 IPC_STRUCT_TRAITS_END()