Check if priority actually changed in Tile::SetPriority()

cc/resources/tile_priority.h

 // Copyright 2012 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_RESOURCES_TILE_PRIORITY_H_
 #define CC_RESOURCES_TILE_PRIORITY_H_
 
 #include <limits>
 
 #include "base/memory/ref_counted.h"
@@ skipping 104 matching lines @@
   }
 
   // Calculate the time for the |current_bounds| to intersect with the
   // |target_bounds| given its previous location and time delta.
   // This function should work for both scaling and scrolling case.
   static float TimeForBoundsToIntersect(const gfx::RectF& previous_bounds,
                                         const gfx::RectF& current_bounds,
                                         float time_delta,
                                         const gfx::RectF& target_bounds);
 
+  bool operator ==(const TilePriority& other) const {
+    if (is_live != other.is_live) return false;
+    if (!is_live) return true;  // All non-live priorities are the same.
+    return resolution == other.resolution &&
+        time_to_visible_in_seconds == other.time_to_visible_in_seconds &&
+        distance_to_visible_in_pixels == other.distance_to_visible_in_pixels;
+    // No need to compare current_screen_quad which is for debug only and
+    // never changes by itself.
+  }
+
+  bool operator !=(const TilePriority& other) const {
+    return !(*this == other);
+  }
+
   // If a tile is not live, then all other fields are invalid.
   bool is_live;
   TileResolution resolution;
   float time_to_visible_in_seconds;
   float distance_to_visible_in_pixels;
 
  private:
   gfx::QuadF current_screen_quad;
 };
 
@@ skipping 37 matching lines @@
   size_t memory_limit_in_bytes;
 
   TreePriority tree_priority;
 
   scoped_ptr<base::Value> AsValue() const;
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_TILE_PRIORITY_H_