Make sure to fail PrepareTransfer when the transferables array contains
a non-ArrayBuffer, otherwise the function leaks a scheduled_exception.

Bug: chromium:736565
Change-Id: I64c2e09eb92720519c7bda2dca41749ff5ac9c8d
Reviewed-on: https://chromium-review.googlesource.com/599357
Commit-Queue: Ben Smith <binji@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47141}