cc: Fix layer raster tile iterator not to skip a tile erroneously.

Fix the constructor of the layer raster tile iterator to never advance
a tiling raster tile iterator. This fixes the iterator not to skip the
first tile returned by a tiling raster tile iterator even if there are
no NOW tiles but only SOON and/or EVENTUALLY tiles.

Review URL: https://codereview.chromium.org/555183002

Cr-Commit-Position: refs/heads/master@{#294188}

cc/layers/picture_layer_impl.cc

@@ -1568,7 +1568,7 @@ PictureLayerImpl::LayerRasterTileIterator::LayerRasterTileIterator(
   IteratorType index = stages_[current_stage_].iterator_type;
   TilePriority::PriorityBin tile_type = stages_[current_stage_].tile_type;
   if (!iterators_[index] || iterators_[index].get_type() != tile_type)
-    ++(*this);
+    AdvanceToNextStage();
 }
 
 PictureLayerImpl::LayerRasterTileIterator::~LayerRasterTileIterator() {}
@@ -1584,22 +1584,13 @@ operator++() {
   TilePriority::PriorityBin tile_type = stages_[current_stage_].tile_type;
 
   // First advance the iterator.
-  if (iterators_[index])
-    ++iterators_[index];
-
-  if (iterators_[index] && iterators_[index].get_type() == tile_type)
-    return *this;
+  DCHECK(iterators_[index]);
+  DCHECK(iterators_[index].get_type() == tile_type);
+  ++iterators_[index];
 
-  // Next, advance the stage.
-  ++current_stage_;
-  while (current_stage_ < arraysize(stages_)) {
-    index = stages_[current_stage_].iterator_type;
-    tile_type = stages_[current_stage_].tile_type;
+  if (!iterators_[index] || iterators_[index].get_type() != tile_type)
+    AdvanceToNextStage();
 
-    if (iterators_[index] && iterators_[index].get_type() == tile_type)
-      break;
-    ++current_stage_;
-  }
   return *this;
 }
 
@@ -1623,6 +1614,19 @@ const Tile* PictureLayerImpl::LayerRasterTileIterator::operator*() const {
   return *iterators_[index];
 }
 
+void PictureLayerImpl::LayerRasterTileIterator::AdvanceToNextStage() {
+  DCHECK_LT(current_stage_, arraysize(stages_));
+  ++current_stage_;
+  while (current_stage_ < arraysize(stages_)) {
+    IteratorType index = stages_[current_stage_].iterator_type;
+    TilePriority::PriorityBin tile_type = stages_[current_stage_].tile_type;
+
+    if (iterators_[index] && iterators_[index].get_type() == tile_type)
+      break;
+    ++current_stage_;
+  }
+}
+
 PictureLayerImpl::LayerEvictionTileIterator::LayerEvictionTileIterator()
     : layer_(NULL),
       tree_priority_(SAME_PRIORITY_FOR_BOTH_TREES),

cc/layers/picture_layer_impl.h

@@ -51,6 +51,8 @@ class CC_EXPORT PictureLayerImpl
    private:
     enum IteratorType { LOW_RES, HIGH_RES, NUM_ITERATORS };
 
+    void AdvanceToNextStage();
+
     PictureLayerImpl* layer_;
 
     struct IterationStage {

cc/layers/picture_layer_impl_unittest.cc

@@ -2498,6 +2498,11 @@ TEST_F(PictureLayerImplTest, HighResTilingDuringAnimationForGpuRasterization) {
 }
 
 TEST_F(PictureLayerImplTest, LayerRasterTileIterator) {
+  base::TimeTicks time_ticks;
+  time_ticks += base::TimeDelta::FromMilliseconds(1);
+  host_impl_.SetCurrentBeginFrameArgs(
+      CreateBeginFrameArgsForTesting(time_ticks));
+
   gfx::Size tile_size(100, 100);
   gfx::Size layer_bounds(1000, 1000);
 
@@ -2563,6 +2568,45 @@ TEST_F(PictureLayerImplTest, LayerRasterTileIterator) {
   EXPECT_EQ(low_res_tile_count + high_res_tile_count + non_ideal_tile_count,
             unique_tiles.size());
 
+  // No NOW tiles.
+  time_ticks += base::TimeDelta::FromMilliseconds(200);
+  host_impl_.SetCurrentBeginFrameArgs(
+      CreateBeginFrameArgsForTesting(time_ticks));
+
+  pending_layer_->draw_properties().visible_content_rect =
+      gfx::Rect(1100, 1100, 500, 500);
+  pending_layer_->UpdateTiles(NULL);
+
+  unique_tiles.clear();
+  high_res_tile_count = 0u;
+  for (it = PictureLayerImpl::LayerRasterTileIterator(pending_layer_, false);
+       it;
+       ++it) {
+    Tile* tile = *it;
+    TilePriority priority = tile->priority(PENDING_TREE);
+
+    EXPECT_TRUE(tile);
+
+    // Non-high res tiles only get visible tiles.
+    EXPECT_EQ(HIGH_RESOLUTION, priority.resolution);
+    EXPECT_NE(TilePriority::NOW, priority.priority_bin);
+
+    high_res_tile_count += priority.resolution == HIGH_RESOLUTION;
+
+    unique_tiles.insert(tile);
+  }
+
+  EXPECT_EQ(16u, high_res_tile_count);
+  EXPECT_EQ(high_res_tile_count, unique_tiles.size());
+
+  time_ticks += base::TimeDelta::FromMilliseconds(200);
+  host_impl_.SetCurrentBeginFrameArgs(
+      CreateBeginFrameArgsForTesting(time_ticks));
+
+  pending_layer_->draw_properties().visible_content_rect =
+      gfx::Rect(0, 0, 500, 500);
+  pending_layer_->UpdateTiles(NULL);
+
   std::vector<Tile*> high_res_tiles = high_res_tiling->AllTilesForTesting();
   for (std::vector<Tile*>::iterator tile_it = high_res_tiles.begin();
        tile_it != high_res_tiles.end();