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NEON version of the SSE2 optimizations for the a-rate OscillatorNode.
We see about a 23% increase in performance with these changes according
to Spotify's Web Audio Bench on a Pixel 2.

Without CL
TEST	μs	MIN	Q1	MEDIAN	Q3	MAX	MEAN	STDDEV
Oscillator.frequency-linear-a-rate	5640	5640	5923	6170	6780	7800	6354.266667	511.6527827

With CL
TEST	μs	MIN	Q1	MEDIAN	Q3	MAX	MEAN	STDDEV
Oscillator.frequency-linear-a-rate	4355	4355	4588	4732	5258	6408	4929.9	474.3852906

Manually ran the oscillator tests on a Pixel 2 and update the thresholds.

Bug: 1013118
Change-Id: I37fbb995ec6bef55ae5195f579356b97adb94347
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2293424
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Reviewed-by: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790016}