Add isolate parameter to HandleScope ctor (easy cases).

The default ctor of HandleScope will go away.

BUG=263412
R=haraken@chromium.org

Review URL: https://codereview.chromium.org/19475004

git-svn-id: svn://svn.chromium.org/blink/trunk@154824 bbb929c8-8fbe-4397-9dbb-9b2b20218538