ozone: Reject overlays when a test buffer can't be allocated.

ui/ozone/platform/drm/gpu/mock_scanout_buffer_generator.h

 // 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.
 
 #ifndef UI_OZONE_PLATFORM_DRM_GPU_MOCK_SCANOUT_BUFFER_GENERATOR_H_
 #define UI_OZONE_PLATFORM_DRM_GPU_MOCK_SCANOUT_BUFFER_GENERATOR_H_
 
 #include "base/macros.h"
 
 #include "ui/ozone/platform/drm/gpu/scanout_buffer.h"
 
 namespace ui {
 
 class MockScanoutBufferGenerator : public ScanoutBufferGenerator {
  public:
   MockScanoutBufferGenerator();
   ~MockScanoutBufferGenerator() override;
 
   // ScanoutBufferGenerator:
   scoped_refptr<ScanoutBuffer> Create(const scoped_refptr<DrmDevice>& drm,
                                       uint32_t format,
                                       const gfx::Size& size) override;
 
+  void set_allocation_failure(bool allocation_failure) {
+    allocation_failure_ = allocation_failure;
+  }
+
  private:
   DISALLOW_COPY_AND_ASSIGN(MockScanoutBufferGenerator);
+
+  bool allocation_failure_ = false;
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PLATFORM_DRM_GPU_MOCK_SCANOUT_BUFFER_GENERATOR_H_