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

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

 // Copyright 2015 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/drm_thread.h"
 
 #include "base/command_line.h"
 #include "base/thread_task_runner_handle.h"
 #include "ui/ozone/platform/drm/gpu/drm_buffer.h"
 #include "ui/ozone/platform/drm/gpu/drm_device_generator.h"
@@ skipping 16 matching lines @@
  public:
   GbmBufferGenerator() {}
   ~GbmBufferGenerator() override {}
 
   // ScanoutBufferGenerator:
   scoped_refptr<ScanoutBuffer> Create(const scoped_refptr<DrmDevice>& drm,
                                       gfx::BufferFormat format,
                                       const gfx::Size& size) override {
     scoped_refptr<GbmDevice> gbm(static_cast<GbmDevice*>(drm.get()));
     return GbmBuffer::CreateBuffer(gbm, format, size,
-                                   gfx::BufferUsage::GPU_READ_WRITE);
+                                   gfx::BufferUsage::SCANOUT);
   }
 
  protected:
   DISALLOW_COPY_AND_ASSIGN(GbmBufferGenerator);
 };
 
 class GbmDeviceGenerator : public DrmDeviceGenerator {
  public:
   GbmDeviceGenerator(bool use_atomic) : use_atomic_(use_atomic) {}
   ~GbmDeviceGenerator() override {}
@@ skipping 169 matching lines @@
     const base::Callback<void(int64_t, bool)>& callback) {
   callback.Run(display_id, display_manager_->SetHDCPState(display_id, state));
 }
 
 void DrmThread::SetGammaRamp(int64_t id,
                              const std::vector<GammaRampRGBEntry>& lut) {
   display_manager_->SetGammaRamp(id, lut);
 }
 
 }  // namespace ui