Enable H.264 video WebRTC behind run-time flag and add WebRtcBrowserTest for H.264

chrome/browser/media/DEPS

Index: chrome/browser/media/DEPS
diff --git a/chrome/browser/media/DEPS b/chrome/browser/media/DEPS
index c230b82f8eee2fa3a405d12f5d2f9bd2097379f9..07d8b0741d57699adc5361dd81e1a8742e7d0961 100644
--- a/chrome/browser/media/DEPS
+++ b/chrome/browser/media/DEPS
@@ -1,4 +1,6 @@
 include_rules = [
+  "+content/public/renderer/renderer_features.h",  # For BUILDFLAG(RTC_USE_H264)

[jochen (gone - plz use gerrit), 2016/02/17 10:55:40]

browser can't depend on renderer.

[hbos_chromium, 2016/02/17 12:27:42]

It's only depending on the RTC_USE_H264 buildflag and finch flag (nothing that
is otherwise "renderer").
- Do you suggest moving these? To where? Can I place it in content/public/?

(I defined the flags to be close to peer_connection_dependency_factory.cc which
uses them and initializes webrtc stuff, so it made sense to put the flags for if
they should be enabled there. They're not placed in the webrtc repo because that
repo does not have access to the deps the flag needs. See previous discussion
about the buildflag. Finch flag has not been discussed previously but I placed
it where I did for the same reasons.)

+  "+content/public/renderer/media/webrtc/finch_h264_with_openh264_ffmpeg.h",
   "+media/audio",
   "+media/base",
   "+media/cast",