DevTools: misc UI polish in Layers & Paint Profiler

BUG=

Review URL: https://codereview.chromium.org/682633003

git-svn-id: svn://svn.chromium.org/blink/trunk@184580 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Popover.setCanShrink(true) doesn't work as expected

BUG=428225

Review URL: https://codereview.chromium.org/687183002

git-svn-id: svn://svn.chromium.org/blink/trunk@184581 bbb929c8-8fbe-4397-9dbb-9b2b20218538