Cache viewport rect for tile priority in UpdateTiles

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 041c5fea5186105c11c86371cea45ed66c3ee206..ff9e89616e3999be5305079d95c6902eb2cc52a1 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -561,6 +561,11 @@ bool LayerTreeImpl::UpdateDrawProperties() {
     LayerIteratorType end = LayerIteratorType::End(&render_surface_layer_list_);
     size_t layers_updated_count = 0;
     bool tile_priorities_updated = false;
+    if (!resourceless_software_draw) {
+      viewport_rect_for_tile_priority_ =
+          layer_tree_host_impl_->ViewportRectForTilePriority();

[boliu, 2015/01/15 01:36:05]

I guess this is ok now, but probably safer to move this above the
CalculateDrawProperties? There is no need to check resourceless_software_draw,
this is valid even inside a software draw.

[hush (inactive), 2015/01/15 01:51:59]

Yes. Done.

+    }
+
     for (LayerIteratorType it =
              LayerIteratorType::Begin(&render_surface_layer_list_);
          it != end;
@@ -818,7 +823,7 @@ gfx::Size LayerTreeImpl::DrawViewportSize() const {
 }
 
 const gfx::Rect LayerTreeImpl::ViewportRectForTilePriority() const {
-  return layer_tree_host_impl_->ViewportRectForTilePriority();
+  return viewport_rect_for_tile_priority_;
 }
 
 scoped_ptr<ScrollbarAnimationController>