This eliminates some instances rtc:Optional and makes the code
simpler. No changes in defaults or other behaviour are intended.
BUG=webrtc:4906
Review URL: https://codereview.webrtc.org/1818033002
Cr-Commit-Position: refs/heads/master@{#12326}
all interfaces that formerly took constraints parameters
in name=value form.
This is in preparation for making Chrome only use these
explicit interfaces.
BUG=webrtc:4906
Review URL: https://codereview.webrtc.org/1717583002
Cr-Commit-Position: refs/heads/master@{#11870}
