Fix all -Wnon-virtual-dtor warnings.

webrtc/pc/pc.gyp

Index: webrtc/pc/pc.gyp
diff --git a/webrtc/pc/pc.gyp b/webrtc/pc/pc.gyp
index b07f7b72638e8ed044bdf9e5abbde89ba5cbc3a9..25ebc5de78cf077db2be3d8cf0f3d20c6805b2c2 100755
--- a/webrtc/pc/pc.gyp
+++ b/webrtc/pc/pc.gyp
@@ -33,11 +33,6 @@
       'defines': [
         '<@(rtc_pc_defines)',
       ],
-      # TODO(kjellander): Make the code compile without disabling these flags.
-      # See https://bugs.chromium.org/p/webrtc/issues/detail?id=3307
-      'cflags_cc!': [
-        '-Wnon-virtual-dtor',
-      ],
       'include_dirs': [
         '<(DEPTH)/testing/gtest/include',
       ],
@@ -97,11 +92,6 @@
             'rtcpmuxfilter_unittest.cc',
             'srtpfilter_unittest.cc',
           ],
-          # TODO(kjellander): Make the code compile without disabling these flags.
-          # See https://bugs.chromium.org/p/webrtc/issues/detail?id=3307
-          'cflags_cc!': [
-            '-Wnon-virtual-dtor',
-          ],
           'conditions': [
             ['clang==0', {
               'cflags': [