cc : Set 'needs update' on transform tree only when something changes

cc/trees/property_tree.cc

 // Copyright 2014 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 <stddef.h>
 
 #include <set>
 #include <vector>
 
 #include "base/logging.h"
@@ skipping 661 matching lines @@
   gfx::Vector2dF screen_space_scale =
       MathUtil::ComputeTransform2dScaleComponents(transform, fallback_value);
   DCHECK_NE(screen_space_scale.x(), 0.f);
   DCHECK_NE(screen_space_scale.y(), 0.f);
 
   gfx::Transform root_to_screen;
   root_to_screen.Scale(screen_space_scale.x(), screen_space_scale.y());
   gfx::Transform root_from_screen;
   bool invertible = root_to_screen.GetInverse(&root_from_screen);
   DCHECK(invertible);
-  SetToScreen(kRootNodeId, root_to_screen);
-  SetFromScreen(kRootNodeId, root_from_screen);
-  set_needs_update(true);
+  if (root_to_screen != ToScreen(kRootNodeId)) {
+    SetToScreen(kRootNodeId, root_to_screen);
+    SetFromScreen(kRootNodeId, root_from_screen);
+    set_needs_update(true);
+  }
 
   transform.ConcatTransform(root_from_screen);
   TransformNode* contents_root_node = Node(kContentsRootNodeId);
   if (contents_root_node->post_local != transform) {
     contents_root_node->post_local = transform;
     contents_root_node->needs_local_transform_update = true;
+    set_needs_update(true);
   }
 }
 
 void TransformTree::UpdateInnerViewportContainerBoundsDelta() {
   if (nodes_affected_by_inner_viewport_bounds_delta_.empty())
     return;
 
   set_needs_update(true);
   for (int i : nodes_affected_by_inner_viewport_bounds_delta_)
     Node(i)->needs_local_transform_update = true;
@@ skipping 1519 matching lines @@
 
   const EffectNode* effect_node = effect_tree.Node(effect_id);
 
   bool success = GetFromTarget(transform_id, effect_id, transform);
   transform->Scale(effect_node->surface_contents_scale.x(),
                    effect_node->surface_contents_scale.y());
   return success;
 }
 
 }  // namespace cc