Add visibility flag to GYP.

webrtc/build/common.gypi

Index: webrtc/build/common.gypi
diff --git a/webrtc/build/common.gypi b/webrtc/build/common.gypi
index a349d11088644adc182a818c2b21296baeeb5573..6ec0f1c9426b4105627d813e99fc203b6c66fda7 100644
--- a/webrtc/build/common.gypi
+++ b/webrtc/build/common.gypi
@@ -141,6 +141,12 @@
     # Enabling this may break interop with Android clients that support H264.
     'use_objc_h264%': 0,
 
+    # Enable this to prevent extern symbols from being hidden on iOS builds.
+    # The chromium settings we inherit hide symbols by default on Release
+    # builds. We want our symbols to be visible when distributing WebRTC via
+    # static libraries to avoid linker warnings.
+    'ios_override_visibility%': 0,
+
     # Determines whether QUIC code will be built.
     'use_quic%': 0,
 
@@ -380,6 +386,12 @@
           'WEBRTC_IOS',
         ],
       }],
+      ['OS=="ios" and ios_override_visibility==1', {
+        'xcode_settings': {
+          'GCC_INLINES_ARE_PRIVATE_EXTERN': 'NO',
+          'GCC_SYMBOLS_PRIVATE_EXTERN': 'NO',
+        }
+      }],
       ['OS=="ios" and use_objc_h264==1', {
         'defines': [
           'WEBRTC_OBJC_H264',