Move purging from OnMemoryState to OnPurgeMemory() in cc/

cc/tiles/software_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_SOFTWARE_IMAGE_DECODE_CACHE_H_
 #define CC_TILES_SOFTWARE_IMAGE_DECODE_CACHE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 253 matching lines @@
   void SanityCheckState(int line, bool lock_acquired);
   void RefImage(const ImageKey& key);
   void RefAtRasterImage(const ImageKey& key);
   void UnrefAtRasterImage(const ImageKey& key);
 
   // Helper function which dumps all images in a specific ImageMRUCache.
   void DumpImageMemoryForCache(const ImageMRUCache& cache,
                                const char* cache_name,
                                base::trace_event::ProcessMemoryDump* pmd) const;
 
+  // Removes unlocked decoded images until the number of decoded images is
+  // reduced within the given limit.
+  void ReduceCacheUsageUntilWithinLimit(size_t limit);
+
   // Overriden from base::MemoryCoordinatorClient.
   void OnMemoryStateChange(base::MemoryState state) override;
+  void OnPurgeMemory() override;
 
   // Helper method to get the different tasks. Note that this should be used as
   // if it was public (ie, all of the locks need to be properly acquired).
   bool GetTaskForImageAndRefInternal(const DrawImage& image,
                                      const TracingInfo& tracing_info,
                                      DecodeTaskType type,
                                      scoped_refptr<TileTask>* task);
 
   std::unordered_map<ImageKey, scoped_refptr<TileTask>, ImageKeyHash>
       pending_in_raster_image_tasks_;
@@ skipping 18 matching lines @@
   ResourceFormat format_;
   size_t max_items_in_cache_;
 
   // Used to uniquely identify DecodedImages for memory traces.
   base::AtomicSequenceNumber next_tracing_id_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TILES_SOFTWARE_IMAGE_DECODE_CACHE_H_