ui: Revert gfx::BufferUsage::SCANOUT to gfx::BufferUsage::GPU_READ_WRITE change.

ui/ozone/platform/drm/gpu/gbm_surface_factory.cc

 // Copyright 2014 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.
 
 #include "ui/ozone/platform/drm/gpu/gbm_surface_factory.h"
 
 #include <gbm.h>
 
 #include "base/files/file_path.h"
 #include "third_party/khronos/EGL/egl.h"
@@ skipping 92 matching lines @@
 }
 
 scoped_refptr<ui::NativePixmap> GbmSurfaceFactory::CreateNativePixmap(
     gfx::AcceleratedWidget widget,
     gfx::Size size,
     gfx::BufferFormat format,
     gfx::BufferUsage usage) {
 #if !defined(OS_CHROMEOS)
   // Support for memory mapping accelerated buffers requires some
   // CrOS-specific patches (using vgem).
-  DCHECK(gfx::BufferUsage::GPU_READ == usage ||
-         gfx::BufferUsage::GPU_READ_WRITE == usage);
+  DCHECK(gfx::BufferUsage::SCANOUT == usage);
 #endif
 
   scoped_refptr<GbmBuffer> buffer =
       drm_thread_->CreateBuffer(widget, size, format, usage);
   if (!buffer.get())
     return nullptr;
 
   scoped_refptr<GbmPixmap> pixmap(new GbmPixmap(this));
   if (!pixmap->InitializeFromBuffer(buffer))
     return nullptr;
 
   return pixmap;
 }
 
 scoped_refptr<ui::NativePixmap> GbmSurfaceFactory::CreateNativePixmapFromHandle(
     const gfx::NativePixmapHandle& handle) {
   scoped_refptr<GbmPixmap> pixmap(new GbmPixmap(this));
   pixmap->Initialize(base::ScopedFD(handle.fd.fd), handle.stride);
   return pixmap;
 }
 
 }  // namespace ui