memory coordinator: Add MemoryCoordinatorClient::OnPurgeMemory()

cc/tiles/gpu_image_decode_cache.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 CC_TILES_GPU_IMAGE_DECODE_CACHE_H_
 #define CC_TILES_GPU_IMAGE_DECODE_CACHE_H_
 
 #include <memory>
 #include <unordered_map>
 #include <vector>
@@ skipping 112 matching lines @@
   void ReduceCacheUsage() override;
   void SetShouldAggressivelyFreeResources(
       bool aggressively_free_resources) override;
 
   // MemoryDumpProvider overrides.
   bool OnMemoryDump(const base::trace_event::MemoryDumpArgs& args,
                     base::trace_event::ProcessMemoryDump* pmd) override;
 
   // base::MemoryCoordinatorClient overrides.
   void OnMemoryStateChange(base::MemoryState state) override;
+  void OnPurgeMemory() override;
 
   // Called by Decode / Upload tasks.
   void DecodeImage(const DrawImage& image);
   void UploadImage(const DrawImage& image);
 
   // Called by Decode / Upload tasks when tasks are finished.
   void OnImageDecodeTaskCompleted(const DrawImage& image,
                                   DecodeTaskType task_type);
   void OnImageUploadTaskCompleted(const DrawImage& image);
 
@@ skipping 199 matching lines @@
 
   // We can't release GPU backed SkImages without holding the context lock,
   // so we add them to this list and defer deletion until the next time the lock
   // is held.
   std::vector<sk_sp<SkImage>> images_pending_deletion_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TILES_GPU_IMAGE_DECODE_CACHE_H_