Version 4.3.61.37 (cherry-pick)

Merged b199bcdd

unicode-decoder: fix out-of-band write in utf16

BUG=v8:4274
LOG=N
R=hablich@chromium.org

Review URL: https://codereview.chromium.org/1229143005 .

Cr-Commit-Position: refs/branch-heads/4.3@{#42}
Cr-Branched-From: f5c0a23a-refs/heads/4.3.61@{#1}
Cr-Branched-From: 0a7d4f49-refs/heads/master@{#27508}