b=952756 always remember offset and duration from Start() r=padenot

--HG--
extra : transplant_source : %9A%3D%12wAbL%0D%E1%16G%A9%B7%23%A9%16%7F%8C%2B%18
b=944851 don't consider AudioNode input when getting AudioParam values on the main thread r=ehsan

--HG--
extra : transplant_source : %15o4%BAA%1F%D4%87%01%CD%B3H%A1T%B0%88%27%9F%A1e
b=949683 optimize zero-gain in GainNode r=padenot

--HG--
extra : transplant_source : %97Js%1B%23%13%AEb%7F%9E%B5%C4%BEx%84xV%C1%F7%5B
b=944143 avoid producing infinite stream of subnormals in ZeroPole tail r=padenot

--HG--
extra : transplant_source : gI%94%E9%DB%99%83%B7%09%B6%82q%FF9%5DI%BE%D6%EF%B6
b=956611 remove costly atomic reference counting from ProduceDataForStreamsBlockByBlock r=padenot

--HG--
extra : transplant_source : %D7bP%80%E1zKym%0A6%E2w%FB%22%3Cy%00%23V