Explicitly pass the isolate to static devtools methods

They're invoked not only from the main thread, so we can't know the
right isolate.

BUG=359977
R=yurys@chromium.org

Review URL: https://codereview.chromium.org/227573004

git-svn-id: svn://svn.chromium.org/blink/trunk@170978 bbb929c8-8fbe-4397-9dbb-9b2b20218538