[DevTools] Preserve screen cast sidebar width.

BUG=307603

Review URL: https://codereview.chromium.org/27718003

git-svn-id: svn://svn.chromium.org/blink/trunk@159912 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: bring back gray toolbars, more ui polish.

TBR=vsevik

Review URL: https://codereview.chromium.org/27725002

git-svn-id: svn://svn.chromium.org/blink/trunk@159913 bbb929c8-8fbe-4397-9dbb-9b2b20218538