cc: Add checker-imaging support to TileManager.

cc/trees/layer_tree_settings.h

Index: cc/trees/layer_tree_settings.h
diff --git a/cc/trees/layer_tree_settings.h b/cc/trees/layer_tree_settings.h
index 901832d2a4aa1e4b6763927537b171d2fa788d8c..775cc9d5cd7f0c63e551b2d72a0e855764b1e95f 100644
--- a/cc/trees/layer_tree_settings.h
+++ b/cc/trees/layer_tree_settings.h
@@ -96,6 +96,11 @@ class CC_EXPORT LayerTreeSettings {
   // tiles come before lower priority tiles.
   bool check_tile_priority_inversion = false;
 
+  // If set to true, the compositor may selectively defer image decodes to the
+  // Image Decode Service and raster tiles without images until the decode is
+  // ready.
+  bool enable_checker_imaging = false;
+
   LayerTreeDebugState initial_debug_state;
 };