DevTools: convert "Rendering" section of settings into a drawer.
Drive-by, move Emulation drawer checkbox into Appearance.

R=caseq@chromium.org

Review URL: https://codereview.chromium.org/96943002

git-svn-id: svn://svn.chromium.org/blink/trunk@162912 bbb929c8-8fbe-4397-9dbb-9b2b20218538