diff --git a/webrtc/BUILD.gn b/webrtc/BUILD.gn
index 11020300f3..07f2fe998d 100644
--- a/webrtc/BUILD.gn
+++ b/webrtc/BUILD.gn
@@ -21,7 +21,17 @@ config("common_inherited_config") {
     defines += [ "WEBRTC_MOZILLA_BUILD" ]
   }
   if (build_with_chromium) {
-    defines = [ "WEBRTC_CHROMIUM_BUILD" ]
+    defines = [
+      # TODO(kjellander): Cleanup unused ones and move defines closer to
+      # the source when webrtc:4256 is completed.
+      "FEATURE_ENABLE_SSL",
+      "FEATURE_ENABLE_VOICEMAIL",
+      "EXPAT_RELATIVE_PATH",
+      "GTEST_RELATIVE_PATH",
+      "NO_MAIN_THREAD_WRAPPING",
+      "NO_SOUND_SYSTEM",
+      "WEBRTC_CHROMIUM_BUILD",
+    ]
     include_dirs = [
       # The overrides must be included first as that is the mechanism for
       # selecting the override headers in Chromium.
@@ -51,7 +61,10 @@ config("common_inherited_config") {
     defines += [ "WEBRTC_MAC" ]
   }
   if (is_win) {
-    defines += [ "WEBRTC_WIN" ]
+    defines += [
+      "WEBRTC_WIN",
+      "_CRT_SECURE_NO_WARNINGS",  # Suppress warnings about _vsnprinf
+    ]
   }
   if (is_android) {
     defines += [
@@ -59,6 +72,20 @@ config("common_inherited_config") {
       "WEBRTC_ANDROID",
     ]
   }
+  if (is_chromeos) {
+    defines += [ "CHROMEOS" ]
+  }
+
+  # TODO(GYP): Support these in GN.
+  # if (is_bsd) {
+  #   defines += [ "BSD" ]
+  # }
+  # if (is_openbsd) {
+  #   defines += [ "OPENBSD" ]
+  # }
+  # if (is_freebsd) {
+  #   defines += [ "FREEBSD" ]
+  # }
 }
 
 if (rtc_have_dbus_glib) {
@@ -70,8 +97,10 @@ if (rtc_have_dbus_glib) {
 config("common_config") {
   cflags = []
   cflags_cc = []
+  defines = []
+
   if (rtc_restrict_logging) {
-    defines = [ "WEBRTC_RESTRICT_LOGGING" ]
+    defines += [ "WEBRTC_RESTRICT_LOGGING" ]
   }
 
   if (rtc_have_dbus_glib) {
@@ -85,7 +114,22 @@ config("common_config") {
   }
 
   if (build_with_chromium) {
-    defines += [ "LOGGING_INSIDE_WEBRTC" ]
+    defines += [
+      # NOTICE: Since common_inherited_config is used in public_configs for our
+      # targets, there's no point including the defines in that config here.
+      # TODO(kjellander): Cleanup unused ones and move defines closer to the
+      # source when webrtc:4256 is completed.
+      "ENABLE_EXTERNAL_AUTH",
+      "HAVE_OPENSSL_SSL_H",
+      "HAVE_SCTP",
+      "HAVE_SRTP",
+      "HAVE_WEBRTC_VIDEO",
+      "HAVE_WEBRTC_VOICE",
+      "LOGGING_INSIDE_WEBRTC",
+      "SRTP_RELATIVE_PATH",
+      "SSL_USE_OPENSSL",
+      "USE_WEBRTC_DEV_BRANCH",
+    ]
   } else {
     if (is_posix) {
       # -Wextra is currently disabled in Chromium"s common.gypi. Enable
diff --git a/webrtc/build/common.gypi b/webrtc/build/common.gypi
index 37f8ead389..a45c7adbcc 100644
--- a/webrtc/build/common.gypi
+++ b/webrtc/build/common.gypi
@@ -280,8 +280,22 @@
       ['build_with_chromium==1', {
         'defines': [
           # Changes settings for Chromium build.
-          'WEBRTC_CHROMIUM_BUILD',
+          # TODO(kjellander): Cleanup unused ones and move defines closer to the
+          # source when webrtc:4256 is completed.
+          'ENABLE_EXTERNAL_AUTH',
+          'FEATURE_ENABLE_SSL',
+          'HAVE_OPENSSL_SSL_H',
+          'HAVE_SCTP',
+          'HAVE_SRTP',
+          'HAVE_WEBRTC_VIDEO',
+          'HAVE_WEBRTC_VOICE',
           'LOGGING_INSIDE_WEBRTC',
+          'NO_MAIN_THREAD_WRAPPING',
+          'NO_SOUND_SYSTEM',
+          'SRTP_RELATIVE_PATH',
+          'SSL_USE_OPENSSL',
+          'USE_WEBRTC_DEV_BRANCH',
+          'WEBRTC_CHROMIUM_BUILD',
         ],
         'include_dirs': [
           # Include the top-level directory when building in Chrome, so we can
@@ -460,6 +474,26 @@
            }],
          ],
       }],
+      ['chromeos==1', {
+        'defines': [
+          'CHROMEOS',
+        ],
+      }],
+      ['os_bsd==1', {
+        'defines': [
+          'BSD',
+        ],
+      }],
+      ['OS=="openbsd"', {
+        'defines': [
+          'OPENBSD',
+        ],
+      }],
+      ['OS=="freebsd"', {
+        'defines': [
+          'FREEBSD',
+        ],
+      }],
       ['include_internal_audio_device==1', {
         'defines': [
           'WEBRTC_INCLUDE_INTERNAL_AUDIO_DEVICE',
@@ -482,6 +516,14 @@
         ['build_with_chromium==1', {
           'defines': [
             # Changes settings for Chromium build.
+            # TODO(kjellander): Cleanup unused ones and move defines closer to
+            # the source when webrtc:4256 is completed.
+            'FEATURE_ENABLE_SSL',
+            'FEATURE_ENABLE_VOICEMAIL',
+            'EXPAT_RELATIVE_PATH',
+            'GTEST_RELATIVE_PATH',
+            'NO_MAIN_THREAD_WRAPPING',
+            'NO_SOUND_SYSTEM',
             'WEBRTC_CHROMIUM_BUILD',
           ],
           'include_dirs': [
@@ -509,6 +551,7 @@
         ['OS=="win"', {
           'defines': [
             'WEBRTC_WIN',
+            '_CRT_SECURE_NO_WARNINGS',  # Suppress warnings about _vsnprinf
           ],
         }],
         ['OS=="linux"', {
@@ -529,6 +572,26 @@
             'WEBRTC_POSIX',
           ],
         }],
+        ['chromeos==1', {
+          'defines': [
+            'CHROMEOS',
+          ],
+        }],
+        ['os_bsd==1', {
+          'defines': [
+            'BSD',
+          ],
+        }],
+        ['OS=="openbsd"', {
+          'defines': [
+            'OPENBSD',
+          ],
+        }],
+        ['OS=="freebsd"', {
+          'defines': [
+            'FREEBSD',
+          ],
+        }],
       ],
     },
   }, # target_defaults