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",
+        "//content/public/common:feature_h264_with_openh264_ffmpeg",
+      ]
     }
     if (enable_media_router) {
       sources += [ "../browser/ui/webui/media_router/media_router_dialog_controller_impl_browsertest.cc" ]