cc: Use multiple PrepareTiles approaches

cc/layers/append_quads_data.h

Index: cc/layers/append_quads_data.h
diff --git a/cc/layers/append_quads_data.h b/cc/layers/append_quads_data.h
index 50f58775d48a3c7e101f6d6da466123a814eec2e..2706492666ead49507b10124b3988ac8398e8757 100644
--- a/cc/layers/append_quads_data.h
+++ b/cc/layers/append_quads_data.h
@@ -14,6 +14,7 @@ struct AppendQuadsData {
   AppendQuadsData()
       : num_incomplete_tiles(0),
         num_missing_tiles(0),
+        num_tiles_missing_raster_source(0),
         visible_content_area(0),
         approximated_visible_content_area(0),
         checkerboarded_visible_content_area(0) {}
@@ -23,6 +24,8 @@ struct AppendQuadsData {
   // Set by the layer appending quads.
   int64 num_missing_tiles;
   // Set by the layer appending quads.
+  int64 num_tiles_missing_raster_source;
+  // Set by the layer appending quads.
   int64 visible_content_area;
   // Set by the layer appending quads.
   int64 approximated_visible_content_area;