This improves performance of ArrayBuffer.isView by roughly 2.5x itself,
and enables optimizations across ArrayBuffer.isView calls, i.e. map
checks can be eliminated across. This was discovered in a related Node
pull request (https://github.com/nodejs/node/pull/15663).

Bug: v8:6868
Change-Id: I1d56ec385f8daa0e1d44d3bc4d6c9a5558ba4522
Reviewed-on: https://chromium-review.googlesource.com/691660Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48247}