Avoid calling GetIsolate by passing the Isolate directly to
Accessors::IsJSObjectFieldAccessor.

Bug: v8:7786
Change-Id: I8a3b26080da64110b0c40df63395cab4e85704b7
Reviewed-on: https://chromium-review.googlesource.com/1080808Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53536}