Don't let PaintInvalidationLocationChange shadow other reasons

third_party/WebKit/LayoutTests/fast/repaint/overflow-clip-subtree-layout-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
           "object": "LayoutBlockFlow DIV",
-          "reason": "location change"
+          "reason": "layoutObject insertion"
         }
       ]
     }
   ]
 }