cc: Optimize decode scheduling for checker-images.

cc/tiles/picture_layer_tiling.h

Index: cc/tiles/picture_layer_tiling.h
diff --git a/cc/tiles/picture_layer_tiling.h b/cc/tiles/picture_layer_tiling.h
index ecf1974efa810a069b0dd9792648fd119ba16e39..6882ab77a9b487d2054c656c55168dfcb2ebb022 100644
--- a/cc/tiles/picture_layer_tiling.h
+++ b/cc/tiles/picture_layer_tiling.h
@@ -105,6 +105,10 @@ class CC_EXPORT PictureLayerTiling {
   bool IsTileRequiredForActivation(const Tile* tile) const;
   bool IsTileRequiredForDraw(const Tile* tile) const;
 
+  // Returns true if the tile should be processed for decoding images skipped

[vmpstr, 2017/04/18 00:20:00]

Can you rephrase this a bit (it sounds confusing to me).

Maybe something like

// During raster, some tiles maybe have been rasterized with images skipped. We
still need to process these tiles to ensure we can retrieve the images that need
to be decoded. This function returns true if the given tile is one of these
skipped images tiles that need to processed. 

[Khushal, 2017/04/19 06:16:41]

Its actually not necessary that images were skipped for this tile. Its possible
for a tile on the active tree to become visible while there is a pending tree
tile that will replace it. In which case, we still skip the image for the active
tree tile, but we don't decode it because it won't be present after activation.

That's why I went with ShouldDecodeCheckeredImageForTile, whether we need to
decode the images already skipped, or to be skipped, for this tile.

+  // during rasterization.
+  bool ShouldDecodeCheckeredImagesForTile(const Tile* tile) const;
+
   void set_resolution(TileResolution resolution) {
     resolution_ = resolution;
     may_contain_low_resolution_tiles_ |= resolution == LOW_RESOLUTION;