Android: Don't evict thumbnails for last visible tab on stop

chrome/browser/android/thumbnail/thumbnail_cache.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 CHROME_BROWSER_ANDROID_THUMBNAIL_THUMBNAIL_CACHE_H_
 #define CHROME_BROWSER_ANDROID_THUMBNAIL_THUMBNAIL_CACHE_H_
 
 #include <stddef.h>
 
 #include <list>
 #include <set>
 #include <string>
 
 #include "base/bind.h"
 #include "base/containers/hash_tables.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
+#include "base/memory/memory_pressure_listener.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
 #include "base/time/time.h"
 #include "chrome/browser/android/thumbnail/scoped_ptr_expiring_cache.h"
 #include "chrome/browser/android/thumbnail/thumbnail.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkRefCnt.h"
 #include "ui/android/resources/ui_resource_provider.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/size.h"
@@ skipping 112 matching lines @@
           post_read_task);
   void PostReadTask(TabId tab_id,
                     sk_sp<SkPixelRef> compressed_data,
                     float scale,
                     const gfx::Size& content_size);
   void NotifyObserversOfThumbnailRead(TabId tab_id);
   void RemoveOnMatchedTimeStamp(TabId tab_id, const base::Time& time_stamp);
   static std::pair<SkBitmap, float> CreateApproximation(const SkBitmap& bitmap,
                                                         float scale);
 
+  void OnMemoryPressure(
+      base::MemoryPressureListener::MemoryPressureLevel level);
+
   const size_t compression_queue_max_size_;
   const size_t write_queue_max_size_;
   const bool use_approximation_thumbnail_;
 
   size_t compression_tasks_count_;
   size_t write_tasks_count_;
   bool read_in_progress_;
 
   ExpiringThumbnailCache cache_;
   ExpiringThumbnailCache approximation_cache_;
   base::ObserverList<ThumbnailCacheObserver> observers_;
   ThumbnailMetaDataMap thumbnail_meta_data_;
   TabIdList read_queue_;
   TabIdList visible_ids_;
 
   ui::UIResourceProvider* ui_resource_provider_;
 
+  std::unique_ptr<base::MemoryPressureListener> memory_pressure_;
   base::WeakPtrFactory<ThumbnailCache> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ThumbnailCache);
 };
 
 #endif  // CHROME_BROWSER_ANDROID_THUMBNAIL_THUMBNAIL_CACHE_H_