Add medium image quality to software predecode.

cc/tiles/software_image_decode_controller.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_CONTROLLER_H_
 #define CC_TILES_SOFTWARE_IMAGE_DECODE_CONTROLLER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 213 matching lines @@
   // scaling failed.
   std::unique_ptr<DecodedImage> GetScaledImageDecode(
       const ImageKey& key,
       sk_sp<const SkImage> image);
 
   void SanityCheckState(int line, bool lock_acquired);
   void RefImage(const ImageKey& key);
   void RefAtRasterImage(const ImageKey& key);
   void UnrefAtRasterImage(const ImageKey& key);
 
-  // These functions indicate whether the images can be handled and cached by
-  // ImageDecodeController or whether they will fall through to Skia (with
-  // exception of possibly prerolling them). Over time these should return
-  // "false" in less cases, as the ImageDecodeController should start handling
-  // more of them.
-  bool CanHandleImage(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;
 
   std::unordered_map<ImageKey, scoped_refptr<TileTask>, ImageKeyHash>
       pending_image_tasks_;
 
   // The members below this comment can only be accessed if the lock is held to
   // ensure that they are safe to access on multiple threads.
   base::Lock lock_;
 
   // Decoded images and ref counts (predecode path).
   ImageMRUCache decoded_images_;
   std::unordered_map<ImageKey, int, ImageKeyHash> decoded_images_ref_counts_;
 
   // Decoded image and ref counts (at-raster decode path).
   ImageMRUCache at_raster_decoded_images_;
   std::unordered_map<ImageKey, int, ImageKeyHash>
       at_raster_decoded_images_ref_counts_;
 
   MemoryBudget locked_images_budget_;
 
-  // Note that this is used for cases where the only thing we do is preroll the
-  // image the first time we see it. This mimics the previous behavior and
-  // should over time change as the compositor starts to handle more cases.
-  std::unordered_set<uint32_t> prerolled_images_;
-
   ResourceFormat format_;
 
   // Used to uniquely identify DecodedImages for memory traces.
   base::AtomicSequenceNumber next_tracing_id_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TILES_SOFTWARE_IMAGE_DECODE_CONTROLLER_H_