RenderLayerScrollableArea::updateScrollCornerStyle shouldn't do work if we're using overlay scrollbars

This function showed up on a profile of updateStyle in Silk's toggle_drawer
test case, but there no reason to update the scroll corner style if we're using
overlay scrollbars. If the author has created a custom scrollbar, we'll realize
that we don't have overlay scrollbars.

R=esprehn@chromium.org
BUG=335703

Review URL: https://codereview.chromium.org/178903004

git-svn-id: svn://svn.chromium.org/blink/trunk@168601 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[SVG] remove SVGAnimatedEnumerationPropertyTearOff.h

The file is not being referenced from anywhere. Its functionality was moved to SVGAnimatedEnumeration.h

BUG=349370
TBR=haraken,pdr,fs

Review URL: https://codereview.chromium.org/188413002

git-svn-id: svn://svn.chromium.org/blink/trunk@168602 bbb929c8-8fbe-4397-9dbb-9b2b20218538