Revert of Revert of [Android] Use UIResource for overscroll glow

ui/base/android/system_ui_resource_manager.h

+// 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.
+
+#ifndef UI_BASE_ANDROID_SYSTEM_UI_RESOURCE_MANAGER_H_
+#define UI_BASE_ANDROID_SYSTEM_UI_RESOURCE_MANAGER_H_
+
+#include "cc/resources/ui_resource_client.h"
+#include "ui/base/ui_base_export.h"
+
+namespace ui {
+
+// Interface for loading and accessing shared system UI resources.
+class UI_BASE_EXPORT SystemUIResourceManager {
+ public:
+  enum ResourceType {
+    OVERSCROLL_EDGE = 0,
+    OVERSCROLL_GLOW,
+    RESOURCE_TYPE_FIRST = OVERSCROLL_EDGE,
+    RESOURCE_TYPE_LAST = OVERSCROLL_GLOW
+  };
+
+  virtual ~SystemUIResourceManager() {}
+
+  // Optionally trigger bitmap loading for a given |resource|, if necessary.
+  // Note that this operation may be asynchronous, and subsequent queries to
+  // |GetUIResourceId()| will yield a valid result only after loading finishes.
+  // This method is particularly useful for idly loading a resource before an
+  // explicit cc::UIResourceId is required. Repeated calls will be ignored.
+  virtual void PreloadResource(ResourceType resource) = 0;
+
+  // Return the resource id associated with |resource|. If loading hasn't yet
+  // begun for the given |resource|, it will be triggered immediately. If
+  // loading is asynchronous, 0 will be returned until loading has finished, and
+  // the caller is responsible for re-querying until a valid id is returned.
+  virtual cc::UIResourceId GetUIResourceId(ResourceType resource) = 0;
+};
+
+}  // namespace ui
+
+#endif  // UI_BASE_ANDROID_SYSTEM_UI_RESOURCE_MANAGER_H_