cc: Refactor additional code from BuildRasterQueue.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 43513e79f4d9b370bcd386e9ab86c7493c888fee..4742dc1826230fadf8e37067e024535ff1c2a9af 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -229,7 +229,7 @@ LayerTreeHostImpl::LayerTreeHostImpl(
       gpu_memory_buffer_manager_(gpu_memory_buffer_manager),
       id_(id),
       requires_high_res_to_draw_(false),
-      required_for_draw_tile_is_top_of_raster_queue_(false) {
+      is_likely_to_require_a_draw_(false) {
   DCHECK(proxy_->IsImplThread());
   DidVisibilityChange(this, visible_);
   animation_registrar_->set_supports_scroll_animations(
@@ -1202,20 +1202,6 @@ scoped_ptr<RasterTilePriorityQueue> LayerTreeHostImpl::BuildRasterQueue(
   GetPictureLayerImplPairs(&picture_layer_pairs_, true);
   scoped_ptr<RasterTilePriorityQueue> queue(RasterTilePriorityQueue::Create(
       picture_layer_pairs_, tree_priority, type));
-
-  if (!queue->IsEmpty()) {
-    // Only checking the Top() tile here isn't a definite answer that there is
-    // or isn't something required for draw in this raster queue. It's just a
-    // heuristic to let us hit the common case and proactively tell the
-    // scheduler that we expect to draw within each vsync until we get all the
-    // tiles ready to draw. If we happen to miss a required for draw tile here,
-    // then we will miss telling the scheduler each frame that we intend to draw
-    // so it may make worse scheduling decisions.
-    required_for_draw_tile_is_top_of_raster_queue_ =
-        queue->Top()->required_for_draw();
-  } else {
-    required_for_draw_tile_is_top_of_raster_queue_ = false;
-  }
   return queue;
 }
 
@@ -1229,6 +1215,15 @@ scoped_ptr<EvictionTilePriorityQueue> LayerTreeHostImpl::BuildEvictionQueue(
   return queue;
 }
 
+void LayerTreeHostImpl::SetIsLikelyToRequireADraw(
+    bool is_likely_to_require_a_draw) {
+  // Proactively tell the scheduler that we expect to draw within each vsync
+  // until we get all the tiles ready to draw. If we happen to miss a required
+  // for draw tile here, then we will miss telling the scheduler each frame that
+  // we intend to draw so it may make worse scheduling decisions.
+  is_likely_to_require_a_draw_ = is_likely_to_require_a_draw;
+}
+
 const std::vector<PictureLayerImpl*>& LayerTreeHostImpl::GetPictureLayers()
     const {
   return picture_layers_;
@@ -1242,7 +1237,7 @@ void LayerTreeHostImpl::NotifyReadyToDraw() {
   // Tiles that are ready will cause NotifyTileStateChanged() to be called so we
   // don't need to schedule a draw here. Just stop WillBeginImplFrame() from
   // causing optimistic requests to draw a frame.
-  required_for_draw_tile_is_top_of_raster_queue_ = false;
+  is_likely_to_require_a_draw_ = false;
 
   client_->NotifyReadyToDraw();
 }
@@ -1612,7 +1607,7 @@ void LayerTreeHostImpl::WillBeginImplFrame(const BeginFrameArgs& args) {
   // Cache the begin impl frame interval
   begin_impl_frame_interval_ = args.interval;
 
-  if (required_for_draw_tile_is_top_of_raster_queue_) {
+  if (is_likely_to_require_a_draw_) {
     // Optimistically schedule a draw, as a tile required for draw is at the top
     // of the current raster queue. This will let us expect the tile to complete
     // and draw it within the impl frame we are beginning now.