Don't set -fvisibility=hidden for iOS Debug.

build/config/gcc/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/toolchain/toolchain.gni")
 
 # This config causes functions not to be automatically exported from shared
 # libraries. By default, all symbols are exported but this means there are
 # lots of exports that slow everything down. In general we explicitly mark
 # which functiosn we want to export from components.

[sdefresne, 2016/01/07 11:12:03]

nit: s/functiosn/functions/

 #
 # Some third_party code assumes all functions are exported so this is separated
 # into its own config so such libraries can remove this config to make symbols
 # public again.
 #
 # See http://gcc.gnu.org/wiki/Visibility
 config("symbol_visibility_hidden") {
   # Note that -fvisibility-inlines-hidden is set globally in the compiler
   # config since that can almost always be applied.
   cflags = [ "-fvisibility=hidden" ]
 }
 
+# Set the appropriate default symbol visibility based on existing
+# configurations.
+config("default_symbol_visibility") {
+  # XCTests inject a dynamic library into an iOS application. If fvisibility
+  # is set to hidden, then some symbols from the application needed by XCTests
+  # are not available. Make sure all symbols are exported for Debug
+  # configuration on iOS so XCTests will work.
+  if (!is_ios || is_release) {
+    configs = [ ":symbol_visibility_hidden" ]
+  }
+}
+
 # The rpath is the dynamic library search path. Setting this config on a link
 # step will put the directory where the build generates shared libraries into
 # the rpath.
 #
 # It's important that this *not* be used for release builds we push out.
 # Chrome uses some setuid binaries, and hard links preserve setuid bits. An
 # unprivileged user could gain root privileges by hardlinking a setuid
 # executable and then adding in whatever binaries they want to run into the lib
 # directory.
 #
@@ skipping 45 matching lines @@
       # and the new DT_RUNPATH doesn't work without --no-as-needed flag.
       "-Wl,--disable-new-dtags",
     ]
   }
 }
 
 config("no_exceptions") {
   cflags_cc = [ "-fno-exceptions" ]
   cflags_objcc = cflags_cc
 }