Some cleanup in RenderLayer and LayerPainter.

This addresses some comments from crrev.com/608253005.

BUG=415087

Review URL: https://codereview.chromium.org/619633003

git-svn-id: svn://svn.chromium.org/blink/trunk@183108 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove obsolete canExpandAroundIdeographsInComplexText

Remove the canExpandAroundIdeographsInComplexText flag as is no longer
supported on any platform. As this was the only feature in the
FontPlatformFeatures class this change also removes the class itself.

R=leviw@chromium.org

Review URL: https://codereview.chromium.org/618383003

git-svn-id: svn://svn.chromium.org/blink/trunk@183109 bbb929c8-8fbe-4397-9dbb-9b2b20218538