Clear Image Decode Cache on Navigation

cc/tiles/software_image_decode_cache.h

Index: cc/tiles/software_image_decode_cache.h
diff --git a/cc/tiles/software_image_decode_cache.h b/cc/tiles/software_image_decode_cache.h
index 9032385278dd3207dd2fcad71f86daae236ae9a7..f29c47c4e12b9dffbfe8186b02440c6524f7e0a7 100644
--- a/cc/tiles/software_image_decode_cache.h
+++ b/cc/tiles/software_image_decode_cache.h
@@ -130,6 +130,7 @@ class CC_EXPORT SoftwareImageDecodeCache
   // Software doesn't keep outstanding images pinned, so this is a no-op.
   void SetShouldAggressivelyFreeResources(
       bool aggressively_free_resources) override {}
+  void ClearCache() override;
 
   // Decode the given image and store it in the cache. This is only called by an
   // image decode task from a worker thread.
@@ -143,6 +144,8 @@ class CC_EXPORT SoftwareImageDecodeCache
   bool OnMemoryDump(const base::trace_event::MemoryDumpArgs& args,
                     base::trace_event::ProcessMemoryDump* pmd) override;
 
+  size_t GetNumCacheEntriesForTesting() const { return decoded_images_.size(); }
+
  private:
   // DecodedImage is a convenience storage for discardable memory. It can also
   // construct an image out of SkImageInfo and stored discardable memory.