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 248391c7a3433af2353e3609bc5a154f7570fbcd..393468d2f65a7b9f6ab3c06e09046eae5aa874d5 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -238,7 +238,6 @@ void PictureLayerImpl::AppendQuads(
         color = DebugColors::MissingTileBorderColor();
         width = DebugColors::MissingTileBorderWidth(layer_tree_impl());
       }
-
       scoped_ptr<DebugBorderDrawQuad> debug_border_quad =
           DebugBorderDrawQuad::Create();
       gfx::Rect geometry_rect = iter.geometry_rect();
@@ -281,8 +280,10 @@ void PictureLayerImpl::AppendQuads(
           gfx::Rect opaque_rect = iter->opaque_rect();
           opaque_rect.Intersect(geometry_rect);
 
-          if (iter->contents_scale() != ideal_contents_scale_)
+          if (iter->contents_scale() != ideal_contents_scale_) {
             append_quads_data->had_incomplete_tile = true;
+            append_quads_data->num_incomplete_tiles++;
+          }
 
           scoped_ptr<TileDrawQuad> quad = TileDrawQuad::Create();
           quad->SetNew(shared_quad_state,
@@ -359,6 +360,7 @@ void PictureLayerImpl::AppendQuads(
 
       append_quads_data->num_missing_tiles++;
       append_quads_data->had_incomplete_tile = true;
+      append_quads_data->num_incomplete_tiles++;
       append_quads_data->approximated_visible_content_area +=
           visible_geometry_rect.width() * visible_geometry_rect.height();
       ++missing_tile_count;