DevTools: Optimize debugger stack traces: use frameMirror.allScropes.

Use the new frameMirror.allScopes() instead of fetching the scopes one by one.
Iterating scopes is very expensive on the V8 side, so do this once for each call frame
instead of each scope of a call frame.

This will boost the speed up to 35%!

BUG=340285
R=yurys

Review URL: https://codereview.chromium.org/198873002

git-svn-id: svn://svn.chromium.org/blink/trunk@169225 bbb929c8-8fbe-4397-9dbb-9b2b20218538