Revert 290359 "Remove AudioBuffersState class."

Revert 290359 "Remove AudioBuffersState class."

Broke ChromeOS bots
http://build.chromium.org/p/chromium.chrome/builders/Google%20Chrome%20ChromeOS/builds/70835/steps/compile/logs/stdio#error1

> Remove AudioBuffersState class.
> 
> The AudioBuffersState object doesn't appear to be necessary anymore.
> Most code either completely ignores this information or doesn't actually
> care about the difference between pending_bytes and hardware_delay_bytes.
> Also usually only one of the 2 fields was actually being used at a time.
> This change removes the class and simply uses an int that represent the
> total number of delay bytes.
> 
> BUG=125685
> 
> Review URL: https://codereview.chromium.org/467833002

TBR=acolwell@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=290376

[acolwell GONE FROM CHROMIUM, 2014-08-18 22:08:28]

Committed patchset #1 manually as r290376.