Currently we record at the system default sample rate and convert it to the
sample rate required by whispernet. This is no longer needed since Whispernet
now accepts a "broadcast sample rate" which can be different than the encoding
sample rate. To avoid the expensive resampling, we now need to pass the samples
to Whispernet without conversion and tell whispernet what the recording sample
rate was.

Also change the tests to test this functionality.

Reviews requested,
ckehoe@ - General review.
dalecurtis@ - DEPS review for //media

R=ckehoe@chromium.org, dalecurtis@chromium.org
BUG=454885

Review URL: https://codereview.chromium.org/940123004

Cr-Commit-Position: refs/heads/master@{#317411}