The ObjectIsArrayBuffer simplified operator, which is used to implement
the ArrayBuffer.isView() builtin, didn't have any test coverage.

Bug: v8:8015
Change-Id: Ia15e35bc4ae61627137f7a89976560a8d3db771f
Reviewed-on: https://chromium-review.googlesource.com/1238215Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56112}