cc: Optimize OnePriorityRectIterator a little bit.

This is a pretty small optimization, but it saves a few struct
copies, which seems to make a small difference (~1% improvement) in a
targeted perftest that runs this function.

R=enne
BUG=488636

Review URL: https://codereview.chromium.org/1130343005

Cr-Commit-Position: refs/heads/master@{#330637}

cc/tiles/tiling_set_raster_queue_all.cc

@@ -158,14 +158,18 @@ TilingSetRasterQueueAll::OnePriorityRectIterator::OnePriorityRectIterator(
 template <typename TilingIteratorType>
 void TilingSetRasterQueueAll::OnePriorityRectIterator::AdvanceToNextTile(
     TilingIteratorType* iterator) {
-  bool found_tile = false;
-  while (!found_tile) {
+  for (;;) {
     ++(*iterator);
     if (!(*iterator)) {
       current_tile_ = PrioritizedTile();
       break;
     }
-    found_tile = GetFirstTileAndCheckIfValid(iterator);
+    Tile* tile = tiling_->TileAt(iterator->index_x(), iterator->index_y());
+    if (IsTileValid(tile)) {
+      tiling_->UpdateRequiredStatesOnTile(tile);
+      current_tile_ = tiling_->MakePrioritizedTile(tile, priority_rect_type_);
+      break;
+    }
   }
 }
 
@@ -173,20 +177,26 @@ template <typename TilingIteratorType>
 bool TilingSetRasterQueueAll::OnePriorityRectIterator::
     GetFirstTileAndCheckIfValid(TilingIteratorType* iterator) {
   Tile* tile = tiling_->TileAt(iterator->index_x(), iterator->index_y());
-  if (!tile || !TileNeedsRaster(tile)) {
+  if (!IsTileValid(tile)) {
     current_tile_ = PrioritizedTile();
     return false;
   }
+  tiling_->UpdateRequiredStatesOnTile(tile);
+  current_tile_ = tiling_->MakePrioritizedTile(tile, priority_rect_type_);
+  return true;
+}
+
+bool TilingSetRasterQueueAll::OnePriorityRectIterator::IsTileValid(
+    const Tile* tile) const {
+  if (!tile || !TileNeedsRaster(tile))
+    return false;
   // After the pending visible rect has been processed, we must return false
   // for pending visible rect tiles as tiling iterators do not ignore those
   // tiles.
   if (priority_rect_type_ > PictureLayerTiling::PENDING_VISIBLE_RECT &&
       tiling_->pending_visible_rect().Intersects(tile->content_rect())) {
-    current_tile_ = PrioritizedTile();
     return false;
   }
-  tiling_->UpdateRequiredStatesOnTile(tile);
-  current_tile_ = tiling_->MakePrioritizedTile(tile, priority_rect_type_);
   return true;
 }
 

cc/tiles/tiling_set_raster_queue_all.h

@@ -41,7 +41,7 @@ class CC_EXPORT TilingSetRasterQueueAll {
 
    protected:
     ~OnePriorityRectIterator() = default;
-    bool TileNeedsRaster(Tile* tile) const {
+    bool TileNeedsRaster(const Tile* tile) const {
       return tile->draw_info().NeedsRaster() && !tiling_->IsTileOccluded(tile);
     }
 
@@ -49,6 +49,7 @@ class CC_EXPORT TilingSetRasterQueueAll {
     void AdvanceToNextTile(TilingIteratorType* iterator);
     template <typename TilingIteratorType>
     bool GetFirstTileAndCheckIfValid(TilingIteratorType* iterator);
+    bool IsTileValid(const Tile* tile) const;
 
     PrioritizedTile current_tile_;
     PictureLayerTiling* tiling_;