cc: Optimize decode scheduling for checker-images.

cc/tiles/tile_manager.cc

Index: cc/tiles/tile_manager.cc
diff --git a/cc/tiles/tile_manager.cc b/cc/tiles/tile_manager.cc
index 9a63601f1518184dd63558e00ee15bddb0943dc2..9e5d3558f73d4f005d2f095ed9f6737f3b6888f5 100644
--- a/cc/tiles/tile_manager.cc
+++ b/cc/tiles/tile_manager.cc
@@ -691,7 +691,7 @@ TileManager::PrioritizedWorkToSchedule TileManager::AssignGpuMemoryToTiles() {
     tile->scheduled_priority_ = schedule_priority++;
 
     DCHECK(tile->draw_info().mode() == TileDrawInfo::OOM_MODE ||
-           !tile->draw_info().IsReadyToDraw());
+           !tile->draw_info().IsReadyToDraw() || tile->is_checker_imaged());
 
     // If the tile already has a raster_task, then the memory used by it is
     // already accounted for in memory_usage. Otherwise, we'll have to acquire
@@ -801,6 +801,7 @@ void TileManager::ScheduleTasks(
   size_t priority = kTileTaskPriorityBase;
 
   graph_.Reset();
+  checker_image_tracker_.ResetImageDecodeQueue();
 
   gfx::ColorSpace target_color_space = client_->GetTileColorSpace();
 
@@ -819,7 +820,20 @@ void TileManager::ScheduleTasks(
     Tile* tile = prioritized_tile.tile();
 
     DCHECK(tile->draw_info().requires_resource());
-    DCHECK(!tile->draw_info().resource());
+    DCHECK(!tile->draw_info().resource() || tile->is_checker_imaged());
+
+    bool process_tile_for_checker_images_only = tile->draw_info().resource();

[vmpstr, 2017/03/06 20:45:25]

This seems a bit awkward: "if a tile has a resource then process tile for
checker images" seems to conflate unrelated concepts.

[Khushal, 2017/03/07 00:31:09]

May be this could be
bool process_tile_for_checker_images_only = tile->draw_info().resource() &&
tile->is_checker_imaged() to make it obvious?

+    if (process_tile_for_checker_images_only) {
+      std::vector<DrawImage> images;
+      ImageIdFlatSet checkered_images;
+      prioritized_tile.raster_source()->GetDiscardableImagesInRect(
+          tile->enclosing_layer_rect(), tile->contents_scale(), &images);
+      checker_image_tracker_.FilterImagesForCheckeringForTile(

[vmpstr, 2017/03/06 20:45:25]

It's not clear to me what this is doing, since both of the vectors are
discarded?

[Khushal, 2017/03/07 00:31:09]

Its filtering the images in the tile with the CheckerImageTracker so it can
re-build its internal queue. May be a different name for the Filter function
since it makes this queue as well?

+          &images, &checkered_images, tile->tiling()->tree());
+      DCHECK(!checkered_images.empty())
+          << "Checker-imaged state is sticky on a Tile";
+      continue;
+    }
 
     if (!tile->raster_task_) {
       tile->raster_task_ =
@@ -970,6 +984,8 @@ scoped_refptr<TileTask> TileManager::CreateRasterTask(
         tile->enclosing_layer_rect(), tile->contents_scale(), &images);
     checker_image_tracker_.FilterImagesForCheckeringForTile(
         &images, &images_to_skip, prioritized_tile.tile()->tiling()->tree());
+    if (!images_to_skip.empty())
+      tile->set_is_checker_imaged();
   }
 
   // We can skip the image hijack canvas if we have no images, or no images to