Fix link highlights on links that contain images.

LayoutTests/compositing/gestures/resources/link-highlight-style.css

 /*Used for applying style to a <span> so it looks like a highlight*/
 .fauxHighlight {
   -webkit-border-radius: 3px;
   background-color: rgb(0, 255, 0);
   color: rgb(0, 255, 0);
 }
 
 .fauxHighlightSquare {
   background-color: rgb(0, 255, 0);
   color: rgb(0, 255, 0);
@@ skipping 20 matching lines @@
 }
 
 /*Used for a floating DIV simulating a highlight*/
 .highlightDiv {
   -webkit-border-radius: 3px;
   background-color: rgb(0, 255, 0);
   z-index: 1;
   position: absolute;
 }
 
+.squaredHighlight {
+  -webkit-border-radius: 0px;
+}
+
 .composited {
   -webkit-transform: translateZ(0);
 }