Add tests for closing a frame within the scope of a getusermedia callback.

BUG=472617, 474370

Review URL: https://codereview.chromium.org/1073783003

Cr-Commit-Position: refs/heads/master@{#324633}
  WebRtcGetUserMediaBrowserTest() : trace_log_(NULL) {}

  WebRtcGetUserMediaBrowserTest() : trace_log_(NULL) {}
