[Chromecast] Make CastAudioOutputStream more permissive about queued data
[Chromecast] Make CastAudioOutputStream more permissive about queued data

Previously CastAudioOutputStream attempted to push another buffer exactly
when it "should be" pushed (right after the previous buffer should have
been fully consumed). This was likely to cause underruns due to timer
inaccuracy. This changes it to allow up to about 1 second of queued data.

BUG= internal b/24614509

Review URL: https://codereview.chromium.org/1414913004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#356452}

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