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Per discussions with the Android team they recommend we skip resampling
when using low power audio. This CL expands the workaround we already
have in place for ChromeOS into a more maintable state by introducing
AudioLatency::IsResamplingPassthroughSupported(). This method returns
true on ChromeOS and on Android when the right criteria are met.

There are several changes to the buffering size logic, but none should
result in any actual changes to the buffering size outside of the new
pass-through case. The pass-through case will prefer the larger of the
hardware buffer size or ~20ms to avoid issues with massive bluetooth
output buffers.

As part of this change I've cleaned up the logic in the mixer manager
for determining when to allow passthrough.

Per a battor run done by liberato@ this is a ~34% power reduction (!),
with a basic mp3 playback going from 0.265W to 0.175W.

BUG=731860,747541
TEST=verified resampling is not invoked for basic playback.

Change-Id: Ia885f41bc50d6fe36934587d34ae646d1ef89364
Reviewed-on: https://chromium-review.googlesource.com/590737
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491784}