When constructing a TypedArray by length, only actually setup the
JSTypedArray instance once the buffer is allocated, as only at that
time it's known whether the byte length is fine. Otherwise we confuse
the heap verifier.

Bug: chromium:887891
Change-Id: I407ff9a2a053dd11ef764e4e32f482abb27eb0a8
Reviewed-on: https://chromium-review.googlesource.com/1238494Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56131}