Add commandline flag to enable GCM cipher suites from RFC 7714 in WebRTC.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 0c03ffd47cdbb79e8029f692995f52ddec7b080c..7eceb0b3f87370cef399a011c5e23c40fe1e517f 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -799,6 +799,9 @@ const FeatureEntry kFeatureEntries[] = {
     {"enable-webrtc-hw-h264-encoding", IDS_FLAGS_WEBRTC_HW_H264_ENCODING_NAME,
      IDS_FLAGS_WEBRTC_HW_H264_ENCODING_DESCRIPTION, kOsAndroid | kOsCrOS,
      FEATURE_VALUE_TYPE(features::kWebRtcHWH264Encoding)},
+    {"enable-webrtc-gcm", IDS_FLAGS_WEBRTC_GCM_NAME,
+     IDS_FLAGS_WEBRTC_GCM_DESCRIPTION, kOsAll,
+     SINGLE_VALUE_TYPE(switches::kEnableWebRtcGcm)},
     {"enable-webrtc-stun-origin", IDS_FLAGS_WEBRTC_STUN_ORIGIN_NAME,
      IDS_FLAGS_WEBRTC_STUN_ORIGIN_DESCRIPTION, kOsAll,
      SINGLE_VALUE_TYPE(switches::kEnableWebRtcStunOrigin)},