DevTools: Separate restoring breakpoints when uiSourceCode is added from actually setting them in the debugger when source mapping is changed.

BUG=286267

Review URL: https://codereview.chromium.org/24266005

git-svn-id: svn://svn.chromium.org/blink/trunk@158816 bbb929c8-8fbe-4397-9dbb-9b2b20218538