cc: Throttle tile priority updates to once a frame.

cc/picture_layer_impl.cc

Index: cc/picture_layer_impl.cc
diff --git a/cc/picture_layer_impl.cc b/cc/picture_layer_impl.cc
index 97a79f4f16a56e255c889bc8fa22f2074d151e3e..22d0653ddccdea0df5b8e23965422e98648dcfe0 100644
--- a/cc/picture_layer_impl.cc
+++ b/cc/picture_layer_impl.cc
@@ -27,7 +27,8 @@ namespace cc {
 PictureLayerImpl::PictureLayerImpl(LayerTreeImpl* treeImpl, int id)
     : LayerImpl(treeImpl, id),
       pile_(PicturePileImpl::Create()),
-      last_update_time_(0),
+      last_source_frame_number_(0),
+      last_impl_frame_time_(0),
       last_content_scale_(0),
       ideal_contents_scale_(0),
       is_mask_(false) {
@@ -66,6 +67,10 @@ void PictureLayerImpl::pushPropertiesTo(LayerImpl* base_layer) {
   layer_impl->SetIsMask(is_mask_);
   layer_impl->TransferTilingSet(tilings_.Pass());
   layer_impl->pile_ = pile_;
+  // Sync over the last source frame number so the active tree does not respond
+  // to the source frame number changing in its tree.
+  layer_impl->last_source_frame_number_ = last_source_frame_number_;
+  layer_impl->last_impl_frame_time_ = last_impl_frame_time_;
   pile_ = PicturePileImpl::Create();
   pile_->set_slow_down_raster_scale_factor(
       layerTreeImpl()->debug_state().slowDownRasterScaleFactor);
@@ -197,16 +202,33 @@ void PictureLayerImpl::dumpLayerProperties(std::string*, int indent) const {
   // TODO(enne): implement me
 }
 
-void PictureLayerImpl::didUpdateTransforms() {
+void PictureLayerImpl::updateTilePriorities() {
+  int current_source_frame_number = layerTreeImpl()->source_frame_number();
+  bool first_update_in_new_source_frame =
+      current_source_frame_number != last_source_frame_number_;
+
+  double current_frame_time =
+      (base::TimeTicks::Now() - base::TimeTicks()).InSecondsF();
+  bool first_update_in_new_impl_frame =
+      current_frame_time != last_impl_frame_time_;
+
+  // In pending tree, this is always called. We update priorities:
+  // - Immediately after a commit (first_update_in_new_source_frame).
+  // - On animation ticks after the first frame in the tree
+  //   (first_update_in_new_impl_frame).
+  // In active tree, this is only called during draw. We update priorities:
+  // - On draw if properties were not already computed by the pending tree
+  //   and activated for the frame (first_update_in_new_impl_frame).
+  if (!first_update_in_new_impl_frame && !first_update_in_new_source_frame)
+    return;
+
   gfx::Transform current_screen_space_transform =
       screenSpaceTransform();
-  double current_time =
-      (base::TimeTicks::Now() - base::TimeTicks()).InSecondsF();
   double time_delta = 0;
-  if (last_update_time_ != 0 && last_bounds_ == bounds() &&
+  if (last_impl_frame_time_ != 0 && last_bounds_ == bounds() &&
       last_content_bounds_ == contentBounds() &&
       last_content_scale_ == contentsScaleX()) {
-    time_delta = current_time - last_update_time_;
+    time_delta = current_frame_time - last_impl_frame_time_;
   }
   WhichTree tree = layerTreeImpl()->IsActiveTree() ? ACTIVE_TREE : PENDING_TREE;
   tilings_->UpdateTilePriorities(
@@ -218,8 +240,9 @@ void PictureLayerImpl::didUpdateTransforms() {
       current_screen_space_transform,
       time_delta);
 
+  last_source_frame_number_ = current_source_frame_number;
   last_screen_space_transform_ = current_screen_space_transform;
-  last_update_time_ = current_time;
+  last_impl_frame_time_ = current_frame_time;
   last_bounds_ = bounds();
   last_content_bounds_ = contentBounds();
   last_content_scale_ = contentsScaleX();