Adds media::AudioPullFifo class to Chrome.

Adds media::AudioPullFifo class to Chrome.

A FIFO (First In First Out) buffer to handle mismatches in buffer sizes
between a provider and consumer. The consumer will pull data from this FIFO.
If data is already available in the FIFO, it is provided to the consumer.
If insufficient data is available to satisfy the request, the FIFO will ask
the provider for more data to fulfill a request.

Patch by henrika@chromium.org:
http://codereview.chromium.org/10915123/

BUG=none
TEST=--gtest_filter=AudioPullFifoTest.*
TBR=henrika

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=155744

[henrika (OOO until Aug 14), 2012-09-10 16:16:57]

LGTM.