WebGL: Tidy up buffer allocation logic

gpu/command_buffer/common/gpu_memory_buffer_support.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 GPU_COMMAND_BUFFER_COMMON_GPU_MEMORY_BUFFER_SUPPORT_H_
 #define GPU_COMMAND_BUFFER_COMMON_GPU_MEMORY_BUFFER_SUPPORT_H_
 
 #include "gpu/gpu_export.h"
 #include "ui/gfx/buffer_types.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/gpu_memory_buffer.h"
 
 namespace gpu {
 
 struct Capabilities;
 
-// Returns a valid GpuMemoryBuffer format given a valid internalformat as
-// defined by CHROMIUM_image.
-GPU_EXPORT gfx::BufferFormat DefaultBufferFormatForImageFormat(
-    unsigned internalformat);
-
 // Returns true if |internalformat| is compatible with |format|.
 GPU_EXPORT bool IsImageFormatCompatibleWithGpuMemoryBufferFormat(
     unsigned internalformat,
     gfx::BufferFormat format);
 
 // Returns true if creating an image for a GpuMemoryBuffer with |format| is
 // supported by |capabilities|.
 GPU_EXPORT bool IsImageFromGpuMemoryBufferFormatSupported(
     gfx::BufferFormat format,
     const Capabilities& capabilities);
 
 // Returns true if |size| is valid for |format|.
 GPU_EXPORT bool IsImageSizeValidForGpuMemoryBufferFormat(
     const gfx::Size& size,
     gfx::BufferFormat format);
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_COMMON_GPU_MEMORY_BUFFER_SUPPORT_H_