DevTools: [CodeMirror] handle new-lines in error popovers

Add support to new-line character handling in error and warning console
message texts which are shown in a popover in editor.

BUG=404380
R=vsevik

Review URL: https://codereview.chromium.org/478963002

git-svn-id: svn://svn.chromium.org/blink/trunk@180413 bbb929c8-8fbe-4397-9dbb-9b2b20218538