Add iOS static library GN build script.

webrtc/build/webrtc.gni

 # Copyright (c) 2014 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/arm.gni")
 import("//build/config/features.gni")
@@ skipping 114 matching lines @@
   # FFmpeg must be initialized for |H264DecoderImpl| to work. This can be done
   # by WebRTC during |H264DecoderImpl::InitDecode| or externally. FFmpeg must
   # only be initialized once. Projects that initialize FFmpeg externally, such
   # as Chromium, must turn this flag off so that WebRTC does not also
   # initialize.
   rtc_initialize_ffmpeg = !build_with_chromium
 
   # Build sources requiring GTK. NOTICE: This is not present in Chrome OS
   # build environments, even if available for Chromium builds.
   rtc_use_gtk = !build_with_chromium
+
+  # Enable this to make all symbols visible when building static library
+  # targets.
+  rtc_override_visibility = false
 }
 
 # A second declare_args block, so that declarations within it can
 # depend on the possibly overridden variables in the first
 # declare_args block.
 declare_args() {
   # Include the iLBC audio codec?
   rtc_include_ilbc = !(build_with_chromium || build_with_mozilla)
 
   rtc_restrict_logging = build_with_chromium
@@ skipping 60 matching lines @@
 }
 
 set_defaults("rtc_static_library") {
   configs = rtc_add_configs
   suppressed_configs = []
 }
 
 set_defaults("rtc_shared_library") {
   configs = rtc_add_configs
   suppressed_configs = []
+  if (rtc_override_visibility) {
+    configs += [ "//build/config/gcc:symbol_visibility_default" ]
+    suppressed_configs += [ "//build/config/gcc:symbol_visibility_hidden" ]
+  }
 }
 
 template("rtc_test") {
   test(target_name) {
     forward_variables_from(invoker,
                            "*",
                            [
                              "configs",
                              "public_configs",
                              "suppressed_configs",
@@ skipping 81 matching lines @@
                            ])
     configs += invoker.configs
     configs -= rtc_remove_configs
     configs -= invoker.suppressed_configs
     public_configs = [ rtc_common_inherited_config ]
     if (defined(invoker.public_configs)) {
       public_configs += invoker.public_configs
     }
   }
 }