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..4f55912f68ec20c8eb7660c4f09717440130bdaa 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -878,6 +878,7 @@ if (!is_android) {
       "//components/strings",
       "//components/translate/core/common",
       "//components/user_manager:test_support",
+      "//content/public/common:common_features",
       "//content/test:browsertest_base",
       "//crypto:platform",
       "//crypto:test_support",
@@ -1086,7 +1087,9 @@ if (!is_android) {
     if (enable_captive_portal_detection) {
       sources += [ "../browser/captive_portal/captive_portal_browsertest.cc" ]
     }
-    if (!enable_webrtc) {
+    if (enable_webrtc) {
+      deps += [ "//content/public/common:feature_h264_with_openh264_ffmpeg" ]
+    } else {
       sources -= [
         "../browser/extensions/api/webrtc_audio_private/webrtc_audio_private_browsertest.cc",
         "../browser/extensions/api/webrtc_logging_private/webrtc_logging_private_apitest.cc",