Introduce GpuVideoDecodeAcceleratorFactory.

content/public/common/gpu_video_decode_accelerator_helpers.h

+// Copyright 2016 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.
+#ifndef CONTENT_PUBLIC_GPU_GPU_VIDEO_DECODE_ACCELERATOR_HELPERS_H_
+#define CONTENT_PUBLIC_GPU_GPU_VIDEO_DECODE_ACCELERATOR_HELPERS_H_
+
+#include "base/callback.h"
+#include "base/memory/weak_ptr.h"
+
+namespace gfx {
+class GLContext;
+}
+
+namespace gl {
+class GLImage;
+}
+
+namespace gpu {
+namespace gles2 {
+class GLES2Decoder;
+}
+}
+
+namespace content {
+
+// Helpers/defines for specific VideoDecodeAccelerator implementations in GPU
+// process. Which callbacks are required depends on the implementation.

[kcwu, 2016/03/01 10:25:06]

However, the client is still tightly coupled with the implementation and must
know what callbacks are required. What if the client passed a dummy callback but
the implementation did call it? See my comments in
android_video_decode_accelerator.cc for example.

[Pawel Osciak, 2016/03/02 07:17:12]

As per offline discussion, moved callback checks to Initialize().

+struct gpu_vda_helpers {

[kcwu, 2016/03/01 10:25:06]

Add comments that what threads can call these callbacks?

And mention these callbacks will be called more than once. (According to
callback.h, callbacks running more than once cannot use with base::Passed). 

[Pawel Osciak, 2016/03/02 07:17:12]

Great comment, thanks.

+  // Return current GLContext.
+  using GetGLContextCb = base::Callback<gfx::GLContext*(void)>;
+
+  // Make the applicable GL context current. To be called by VDAs before
+  // executing any GL calls. Return true on success, false otherwise.
+  using MakeGLContextCurrentCb = base::Callback<bool(void)>;
+
+  // Bind |image| to |client_texture_id| given |texture_target|.
+  // Return true on success, false otherwise.
+  using BindGLImageCb =
+      base::Callback<bool(uint32_t client_texture_id,
+                          uint32_t texture_target,
+                          const scoped_refptr<gl::GLImage>& image)>;
+
+  // Return a WeakPtr to a GLES2Decoder, if one is available.
+  using GetGLES2DecoderCb =
+      base::Callback<base::WeakPtr<gpu::gles2::GLES2Decoder>(void)>;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_GPU_GPU_VIDEO_DECODE_ACCELERATOR_HELPERS_H_