Position adjustment for composited scrolling is not needed if the layer has box decorations.

Source/web/LinkHighlight.cpp

Index: Source/web/LinkHighlight.cpp
diff --git a/Source/web/LinkHighlight.cpp b/Source/web/LinkHighlight.cpp
index f19536da70cb34861c45c0f546191f3b34014237..2f51d0c0b93217fc2e492f78eaba94d6dfcf78a2 100644
--- a/Source/web/LinkHighlight.cpp
+++ b/Source/web/LinkHighlight.cpp
@@ -213,7 +213,7 @@ bool LinkHighlight::computeHighlightLayerPathAndPosition(const LayoutBoxModelObj
 
         // FIXME: this hack should not be necessary. It's a consequence of the fact that composited layers for scrolling are represented
         // differently in Blink than other composited layers.
-        if (paintInvalidationContainer->layer()->needsCompositedScrolling() && m_node->layoutObject() != paintInvalidationContainer)
+        if (!paintInvalidationContainer->layer()->hasBoxDecorationsOrBackground() && paintInvalidationContainer->layer()->needsCompositedScrolling() && m_node->layoutObject() != paintInvalidationContainer)

[chrishtr, 2015/04/27 17:50:03]

Can you explain why it's not needed if there are box decorations?

[pals, 2015/04/28 10:28:24]

I am not very familiar of this code. I thought as the composited layer bounds is
larger than the layoutObject()-> absoluteBoundingBoxRect() because of the box
shadow and the highlight is offset by the size of the box shadow. 

[chrishtr, 2015/04/29 05:11:41]

Ok. I'll need to think about this some more. This whole class is in kind of a
sad state. :( 

[chrishtr, 2015/06/06 05:28:09]

I just tried deleting the adjustment hack in lines 216-217 entirely, and all
layout tests passed. Could you update the CL to remove this code, run the tests,
and test various real situations with scrolled areas to make sure they are
correct?

It may be that this hack was compensating for other compositing code, which is
now fixed. Or it could be that we no longer test this situation.. please check
for possible disabled tests of link highlight.

[pals, 2015/06/15 06:01:04]

Done.

             absoluteQuad.move(-positionAdjustForCompositedScrolling.x(), -positionAdjustForCompositedScrolling.y());
 
         // Transform node quads in target absolute coords to local coordinates in the compositor layer.