b=966800 don't ignore blocking changes when another stream is finishing or underrunning r=roc

--HG--
extra : transplant_source : %7C%C3B%08%3E%D2%B2%93%BC%811%22%D1%27%95%AF%BD%D1eB
b=966867 don't overwrite preferred sample rate with default r=kinetik

--HG--
extra : transplant_source : /S%9D/%BC%80%E0%E3%C3%11%E7%EA%D4%BB%F3%D7%AD%06%B7%25
b=966867 use internal linkage for GetSampleRateForAudioContext r=kinetik

--HG--
extra : transplant_source : t%F5%2A%A2%ADbI%40%A3%0E%9FS%D1%FCC%0B%1B%3E%0A%9B