cc: Skip analysis for narrow layers.

cc/resources/tile_manager.cc

Index: cc/resources/tile_manager.cc
diff --git a/cc/resources/tile_manager.cc b/cc/resources/tile_manager.cc
index 8dc9c29ff0ae4527fc343c60bf58bf7b88a6092f..c4e75863fcc40fb5d273556167eeb2e39f35cfc0 100644
--- a/cc/resources/tile_manager.cc
+++ b/cc/resources/tile_manager.cc
@@ -32,6 +32,9 @@ namespace {
 // a tile is of solid color.
 const bool kUseColorEstimator = true;
 
+// Minimum width/height of a pile that would require analysis for tiles.
+const int kMinSizeToAnalyze = 256;

[alokp, 2014/03/27 05:20:45]

kMinLengthToAnalyze?

[vmpstr, 2014/03/27 17:02:53]

Done.

+
 class DisableLCDTextFilter : public SkDrawFilter {
  public:
   // SkDrawFilter interface.
@@ -1163,7 +1166,14 @@ scoped_refptr<internal::RasterWorkerPoolTask> TileManager::CreateRasterTask(
   // It is drawn directly as a solid-color quad saving raster and upload cost.
   // The analysis step is however expensive and is not justified when doing
   // gpu rasterization where there is no upload.
-  bool analyze_picture = !tile->use_gpu_rasterization();
+  //
+  // Additionally, we do not want to do the analysis if the layer that produced
+  // this tile is narrow, since more likely than not the tile would not be

[alokp, 2014/03/27 05:20:45]

I do not get the connection between the tile being narrow and solid. Could you
elaborate this a bit here?

[vmpstr, 2014/03/27 17:02:53]

It definitely doesn't mean that it's not solid, but I think we want to try a
heuristic that just assumes they are not. The example is a page in the bug that
has a lot of small layers, which means we spent all that extra time analyzing
it.

For the majority of the cases (1 root layer, 3 scrollbar layers), this should do
the right thing...

Did you want me to add a more elaborate comment here, or is your concern more
with the whole idea behind this?

[alokp, 2014/03/27 17:45:16]

I understand that it is just a heuristic and I am fine with it. I just wanted a
comment about the justifications for that heuristic.

+  // solid.
+  gfx::Size pile_size = tile->picture_pile()->size();
+  bool analyze_picture =
+      !tile->use_gpu_rasterization() &&
+      std::min(pile_size.width(), pile_size.height()) >= kMinSizeToAnalyze;
 
   return make_scoped_refptr(new RasterWorkerPoolTaskImpl(
       const_resource,