DevTools: Send returning value of a call frame.

Send the returning value to front-end if a call frame is at the return point.

BUG=155730
R=yurys@chromium.org, pfeldman@chromium.org

Review URL: https://codereview.chromium.org/50043005

git-svn-id: svn://svn.chromium.org/blink/trunk@161323 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Totally avoid traversing CSSStyleSheet while inside RuleMutationScope

This resulted in various inspected page crashes during stylesheet text editing.

R=pfeldman, vsevik
BUG=312394

Review URL: https://codereview.chromium.org/51103008

git-svn-id: svn://svn.chromium.org/blink/trunk@161324 bbb929c8-8fbe-4397-9dbb-9b2b20218538