Removes all explicit calls to GetIsolate() in runtime/ by passing it
through calling functions.

Bug: v8:7786
Change-Id: I6485827ea3ef9b215ca487b1f823c9f585f31f98
Reviewed-on: https://chromium-review.googlesource.com/1080747Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53458}