WebRTC: Fix and enable -Woverloaded-virtual warnings.

webrtc/media/BUILD.gn

 # Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("//build/config/linux/pkg_config.gni")
 import("../build/webrtc.gni")
@@ skipping 10 matching lines @@
     "HAVE_WEBRTC_VOICE",
   ]
 }
 
 config("rtc_media_warnings_config") {
   # GN orders flags on a target before flags from configs. The default config
   # adds these flags so to cancel them out they need to come from a config and
   # cannot be on the target directly.
   if (!is_win) {
     cflags = [ "-Wno-deprecated-declarations" ]
-    cflags_cc = [ "-Wno-overloaded-virtual" ]
   }
 }
 
 if (is_linux && rtc_use_gtk) {
   pkg_config("gtk-lib") {
     packages = [
       "gobject-2.0",
       "gthread-2.0",
       "gtk+-2.0",
     ]
@@ skipping 198 matching lines @@
     if (is_clang && is_win) {
       cflags = [
         # See https://bugs.chromium.org/p/webrtc/issues/detail?id=6266
         # for -Wno-sign-compare
         "-Wno-sign-compare",
         "-Wno-unused-function",
       ]
     }
     if (!is_win) {
       cflags = [ "-Wno-sign-compare" ]
-      cflags_cc = [ "-Wno-overloaded-virtual" ]
     }
   }
 
   rtc_media_unittests_resources = [
     "//resources/media/captured-320x240-2s-48.frames",
     "//resources/media/faces.1280x720_P420.yuv",
     "//resources/media/faces_I420.jpg",
     "//resources/media/faces_I422.jpg",
     "//resources/media/faces_I444.jpg",
     "//resources/media/faces_I411.jpg",
@@ skipping 73 matching lines @@
     deps += [
       # TODO(kjellander): Move as part of work in bugs.webrtc.org/4243.
       ":rtc_media",
       ":rtc_unittest_main",
       "../audio",
       "../base:rtc_base_tests_utils",
       "../system_wrappers:metrics_default",
     ]
   }
 }