Create only one ContextFactory in content unit tests

content/browser/compositor/surface_utils.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 CONTENT_BROWSER_COMPOSITOR_SURFACE_UTILS_H_
 #define CONTENT_BROWSER_COMPOSITOR_SURFACE_UTILS_H_
 
 #include <memory>
 
 #include "content/common/content_export.h"
 #include "content/public/browser/readback_types.h"
 #include "third_party/skia/include/core/SkImageInfo.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace cc {
 class CopyOutputResult;
 class SurfaceIdAllocator;
 class SurfaceManager;
 }  // namespace cc
 
 namespace content {
 
+CONTENT_EXPORT
 std::unique_ptr<cc::SurfaceIdAllocator> CreateSurfaceIdAllocator();
 
 CONTENT_EXPORT
 cc::SurfaceManager* GetSurfaceManager();
 
 void CopyFromCompositingSurfaceHasResult(
     const gfx::Size& dst_size_in_pixel,
     const SkColorType color_type,
     const ReadbackRequestCallback& callback,
     std::unique_ptr<cc::CopyOutputResult> result);
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_COMPOSITOR_SURFACE_UTILS_H_