cc: Interface to evict images from cc image decode cache.

cc/tiles/image_decode_cache.h

Index: cc/tiles/image_decode_cache.h
diff --git a/cc/tiles/image_decode_cache.h b/cc/tiles/image_decode_cache.h
index d0bf7be7220f9d6b968ddcd1f299f3d62efdf82a..25ed1404fecb47610a8e86ed3c2ce50f814b5105 100644
--- a/cc/tiles/image_decode_cache.h
+++ b/cc/tiles/image_decode_cache.h
@@ -124,6 +124,12 @@ class CC_EXPORT ImageDecodeCache {
   // memory. It is used as an esimate of whether an image can fit into the
   // locked budget before creating a task.
   virtual size_t GetMaximumMemoryLimitBytes() const = 0;
+
+  // Indicate to the cache that the image is no longer going
+  // to be used. This means it can be deleted altogether. If the
+  // image is locked, then the cache can do its best to clean it
+  // up later.
+  virtual void NotifyImageUnused(uint32_t skimage_id) = 0;
 };
 
 }  // namespace cc