https://codereview.chromium.org/2001393004 makes TypedArray
length property writable, which means we shouldn't depend on it.
Instead, use %_TypedArrayGetLength% to get length.

Attached regression test.

BUG=chromium:615776

Review-Url: https://codereview.chromium.org/2020203006
Cr-Commit-Position: refs/heads/master@{#36655}