Histogram to track missing and incomplete tiles

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 481536b1a04d15bc471dc96c85d63818edd8ce53..b0a62718f3f2d9cfd75ed63bea5e443856d936aa 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -280,7 +280,7 @@ void PictureLayerImpl::AppendQuads(
           opaque_rect.Intersect(geometry_rect);
 
           if (iter->contents_scale() != ideal_contents_scale_)
-            append_quads_data->had_incomplete_tile = true;
+            append_quads_data->num_incomplete_tiles++;
 
           TileDrawQuad* quad =
               render_pass->CreateAndAppendDrawQuad<TileDrawQuad>();
@@ -354,7 +354,6 @@ void PictureLayerImpl::AppendQuads(
       }
 
       append_quads_data->num_missing_tiles++;
-      append_quads_data->had_incomplete_tile = true;
       append_quads_data->approximated_visible_content_area +=
           visible_geometry_rect.width() * visible_geometry_rect.height();
       ++missing_tile_count;