Revert of Fix getUserMedia DCHECK on multiple calls with stopped tracks (patchset...

Revert of Fix getUserMedia DCHECK on multiple calls with stopped tracks (patchset #2 id:40001 of https://codereview.chromium.org/1349273002/ )

Reason for revert:
Speculative revert (could be breaking WebRTC AppRTC test): https://build.chromium.org/p/chromium.webrtc/builders/Mac%20Tester/builds/43297

Original issue's description:
> Fix getUserMedia DCHECK on multiple calls with stopped tracks
>
> There is a race occurring in situations similar to the following:
>
> getUserMedia(
>     {video: true},
>     function(stream) {
>         video_track = stream.getVideoTracks()[0];
>         getUserMedia(...);
>         video_track.stop(); },
>     function() {});
>
> This gets around the issue by postponing GenerateStream until after
> the track has finished stopping. See linked issues for more info.
>
> BUG=532554,525849
>
> Committed: https://crrev.com/aa8ccca3e1b5014807dc8bbc7174fd4ad982f773
> Cr-Commit-Position: refs/heads/master@{#349954}

TBR=perkj@chromium.org,mcasas@chromium.org,emircan@chromium.org,ajose@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=532554,525849

Review URL: https://codereview.chromium.org/1352093003

Cr-Commit-Position: refs/heads/master@{#350131}