cc: Don't draw and swap if the frame will not change.

cc/trees/damage_tracker.cc

 // Copyright 2011 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.
 
 #include "cc/trees/damage_tracker.h"
 
 #include <algorithm>
 
 #include "cc/base/math_util.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
 #include "cc/layers/layer_impl.h"
 #include "cc/layers/render_surface_impl.h"
 #include "cc/trees/layer_tree_host_common.h"
 #include "cc/trees/layer_tree_impl.h"
 #include "third_party/WebKit/Source/Platform/chromium/public/WebFilterOperations.h"
 
 namespace cc {
 
 scoped_ptr<DamageTracker> DamageTracker::Create() {
   return make_scoped_ptr(new DamageTracker());
 }
 
 DamageTracker::DamageTracker()
     : current_rect_history_(new RectMap),
-      next_rect_history_(new RectMap),
-      force_full_damage_next_update_(false) {}
+      next_rect_history_(new RectMap) {}
 
 DamageTracker::~DamageTracker() {}
 
 static inline void ExpandRectWithFilters(
     gfx::RectF* rect, const WebKit::WebFilterOperations& filters) {
   int top, right, bottom, left;
   filters.getOutsets(top, right, bottom, left);
   rect->Inset(-left, -top, -right, -bottom);
 }
 
@@ skipping 91 matching lines @@
   // the damage will be for this frame, because we need to update the damage
   // tracker state to correctly track the next frame.
   gfx::RectF damage_from_active_layers =
       TrackDamageFromActiveLayers(layer_list, target_surface_layer_id);
   gfx::RectF damage_from_surface_mask =
       TrackDamageFromSurfaceMask(target_surface_mask_layer);
   gfx::RectF damage_from_leftover_rects = TrackDamageFromLeftoverRects();
 
   gfx::RectF damage_rect_for_this_update;
 
-  if (force_full_damage_next_update_ ||
-      target_surface_property_changed_only_from_descendant) {
+  if (target_surface_property_changed_only_from_descendant) {
     damage_rect_for_this_update = target_surface_content_rect;
-    force_full_damage_next_update_ = false;
   } else {
     // TODO(shawnsingh): can we clamp this damage to the surface's content rect?
     // (affects performance, but not correctness)
     damage_rect_for_this_update = damage_from_active_layers;
     damage_rect_for_this_update.Union(damage_from_surface_mask);
     damage_rect_for_this_update.Union(damage_from_leftover_rects);
 
     if (filters.hasFilterThatMovesPixels()) {
       ExpandRectWithFilters(&damage_rect_for_this_update, filters);
     } else if (filter) {
@@ skipping 242 matching lines @@
   // one in them. This means we need to redraw any pixels in the surface being
   // used for the blur in this layer this frame.
   if (layer->background_filters().hasFilterThatMovesPixels()) {
     ExpandDamageRectInsideRectWithFilters(target_damage_rect,
                                           surface_rect_in_target_space,
                                           layer->background_filters());
   }
 }
 
 }  // namespace cc