[volumemixer] Chrome/Firefox tab titles in stream name

[Zren]

While this is unrelated to this applet's code, I might as well discuss these features here with links and stuff.

• [ ] Chrome
  • Default behaviour in Windows
  • https://src.chromium.org/viewvc/chrome/trunk/src/media/audio/pulse/pulse_output.cc
  • "Playback" metadata is set at pulse_util.cc Line 262
• [ ] Firefox
  • Default behaviour in Windows
  • Recently went PulseAudio only
  • "Support PulseAudio metadata" issue open on the bug tracker
    https://bugzilla.mozilla.org/show_bug.cgi?id=965653
    • A patch exists that highlights the relevant files
      https://bugzilla.mozilla.org/attachment.cgi?id=8451368&action=diff
  • Source browser: https://dxr.mozilla.org/mozilla-central/source/
    • https://dxr.mozilla.org/mozilla-central/source/media/webrtc/trunk/webrtc/audio/
    • https://dxr.mozilla.org/mozilla-central/source/dom/media/AudioStream.h
    • https://dxr.mozilla.org/mozilla-central/source/dom/media/AudioStream.cpp
  • Firefox uses the cubeb library (blog post)
    https://github.com/kinetiknz/cubeb

The relevant apps will need patching to expose the tab titles.