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

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index ff183c6040778e443e0448eefdffe81312f07e3d..2174d9f8f8e690253421a6d0ffc987f26a6be146 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -878,6 +878,8 @@ if (!is_android) {
       "//components/strings",
       "//components/translate/core/common",
       "//components/user_manager:test_support",
+      "//content/public/common:common_features",
+      "//content/public/common:feature_h264_with_openh264_ffmpeg",
       "//content/test:browsertest_base",
       "//crypto:platform",
       "//crypto:test_support",
@@ -1094,6 +1096,10 @@ if (!is_android) {
         "../browser/media/chrome_webrtc_disable_encryption_flag_browsertest.cc",
         "../browser/media/chrome_webrtc_getmediadevices_browsertest.cc",
       ]
+      deps -= [
+        "//content/public/common:common_features",

[brettw, 2016/02/22 22:50:21]

I don't think there's any downside to keeping common_features when webrtc is
disabled, and we're almost guaranteed that somebody will add more stuff there.
So just remove this line.

[hbos_chromium, 2016/02/23 08:21:04]

Done.

+        "//content/public/common:feature_h264_with_openh264_ffmpeg",

[brettw, 2016/02/22 22:50:21]

Can you flip this so that we include it only when webrtc is enabled?

  if (enable_webrtc) {
    deps += [ "//content/public/common:feature_h264_with_openh264_ffmpeg" ]
  } else {
    ...current non-webrtc code here...
  }

The reason the sources are subtractive is that the sources are read from GYP,
but we don't have that limitation for the deps.

[hbos_chromium, 2016/02/23 08:21:04]

Done. (Yeah that makes a lot more sense)

+      ]
     }
     if (enable_media_router) {
       sources += [ "../browser/ui/webui/media_router/media_router_dialog_controller_impl_browsertest.cc" ]