Version 4.3.61.13 (cherry-pick)

Merged b990a6c6

Turn off SupportsFlexibleFloorAndRound for Arm64 due to a bug.

BUG=chromium:476477
LOG=N
R=erik.corry@gmail.com, erikcorry@chromium.org

Review URL: https://codereview.chromium.org/1107483003

Cr-Commit-Position: refs/branch-heads/4.3@{#16}
Cr-Branched-From: f5c0a23a-refs/heads/4.3.61@{#1}
Cr-Branched-From: 0a7d4f49-refs/heads/master@{#27508}