Provide task runner to GLES2Impl / CommandBuffer at creation

gpu/command_buffer/client/gles2_implementation.cc

 // 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.
 
 // A class to emulate GLES2 over command buffers.
 
 #include "gpu/command_buffer/client/gles2_implementation.h"
 
 #include <GLES2/gl2.h>
 #include <GLES2/gl2ext.h>
@@ skipping 115 matching lines @@
   CHECK_EQ(0, gles2_implementation_->use_count_);
 }
 
 GLES2Implementation::GLES2Implementation(
     GLES2CmdHelper* helper,
     scoped_refptr<ShareGroup> share_group,
     TransferBufferInterface* transfer_buffer,
     bool bind_generates_resource,
     bool lose_context_when_out_of_memory,
     bool support_client_side_arrays,
-    GpuControl* gpu_control)
+    GpuControl* gpu_control,
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner)

[piman, 2016/08/25 22:51:02]

In what way is this task runner meant to be used? I see 2 problems:
1- GLES2Implementation is used in contexts where there is no task runner on the
client thread. For example on the worker thread, as well as in the EGL
implementation for conformance tests and for skia tests.
2- we use the GLES2Implementation on multiple threads, with a lock. This
requires that any task that will use the GLES2Implementation holds the lock
while doing so. So, the client is required to hold that lock when making calls,
and the CommandBufferProxyImpl also takes the lock when executing posted tasks
which would call into the GLES2Implementation - see
CommandBufferProxyImpl::SetLock and uses of that lock. If the
GLES2Implementation is going to post tasks, it will need to take that lock in
those posted tasks, so it will need to be made aware of it.

     : helper_(helper),
       transfer_buffer_(transfer_buffer),
       chromium_framebuffer_multisample_(kUnknownExtensionStatus),
       pack_alignment_(4),
       pack_row_length_(0),
       pack_skip_pixels_(0),
       pack_skip_rows_(0),
       unpack_alignment_(4),
       unpack_row_length_(0),
       unpack_image_height_(0),
@@ skipping 6789 matching lines @@
   cached_extensions_.clear();
 }
 
 // Include the auto-generated part of this file. We split this because it means
 // we can easily edit the non-auto generated parts right here in this file
 // instead of having to edit some template or the code generator.
 #include "gpu/command_buffer/client/gles2_implementation_impl_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu