Let RenderBox's visual overflow include the whole focus ring

Previously visual overflow might not cover the whole focus ring.

Include focus ring in visual overflow to ensure the whole focus ring
is invalidated when needed.

Key change is in RenderBox::computeVisualEffectOverflowExtent().

Other changes are just to add 'const' to addFocusRingRects().

BUG=398512, 396225
TEST=transforms/transform-focus-ring-repaint.html

Review URL: https://codereview.chromium.org/427873002

git-svn-id: svn://svn.chromium.org/blink/trunk@179349 bbb929c8-8fbe-4397-9dbb-9b2b20218538