content: Move shader cache factory singleton into a separate file.

content/browser/gpu/shader_cache_factory.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 CONTENT_BROWSER_GPU_SHADER_CACHE_FACTORY_H_
+#define CONTENT_BROWSER_GPU_SHADER_CACHE_FACTORY_H_
+
+#include "content/browser/gpu/shader_disk_cache.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+// Initializes the ShaderCacheFactory singleton instance. The singleton
+// instance is created and used in the thread associated with |task_runner|.
+// |cache_task_runner| is associated with the thread responsible for managing
+// the disk cache.
+CONTENT_EXPORT void InitShaderCacheFactorySingleton(
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner,
+    scoped_refptr<base::SingleThreadTaskRunner> cache_task_runner);
+
+// Returns an instance previously created by InitShaderCacheFactorySingleton().
+// This can return nullptr if an instance has not yet been created.
+CONTENT_EXPORT ShaderCacheFactory* GetShaderCacheFactorySingleton();
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_GPU_SHADER_CACHE_FACTORY_H_