Enable creation of offscreen contexts which own their backing surface.

gpu/ipc/common/gpu_command_buffer_traits_multi.h

Index: gpu/ipc/common/gpu_command_buffer_traits_multi.h
diff --git a/gpu/ipc/common/gpu_command_buffer_traits_multi.h b/gpu/ipc/common/gpu_command_buffer_traits_multi.h
index 90bb616378f6aad02af91d346ce3aeaf04854f91..0ec21db3cb084ca7ce31c8e268995672fc560e5b 100644
--- a/gpu/ipc/common/gpu_command_buffer_traits_multi.h
+++ b/gpu/ipc/common/gpu_command_buffer_traits_multi.h
@@ -145,4 +145,5 @@ IPC_STRUCT_TRAITS_BEGIN(gpu::gles2::ContextCreationAttribHelper)
   IPC_STRUCT_TRAITS_MEMBER(lose_context_when_out_of_memory)
   IPC_STRUCT_TRAITS_MEMBER(context_type)
   IPC_STRUCT_TRAITS_MEMBER(should_use_native_gmb_for_backbuffer)
+  IPC_STRUCT_TRAITS_MEMBER(own_offscreen_surface)

[bajones, 2017/01/06 23:14:04]

Don't we need to add `low_priority` here?

[klausw, 2017/01/07 00:02:34]

I've added it for consistency. In practice I don't think it
matters, looks like the attributes from the helper get used
in two different paths. Some (including low_priority) are forked 
into gl::GLContextAttributes by service_utils's 
GenerateGLContextAttribs, others are passed down to 
gpu_command_buffer_stub as init_params.attribs, but in this
case this doesn't look at the low_priority attribute.

 IPC_STRUCT_TRAITS_END()