Move Pause on Exception button to sidebar.

BUG=143952

* Moved the Pause on Exception button to the sidebar.
* Remove from status bar items.
* Quick simplification.

Review URL: https://chromiumcodereview.appspot.com/23685008

git-svn-id: svn://svn.chromium.org/blink/trunk@157744 bbb929c8-8fbe-4397-9dbb-9b2b20218538