Get iOS GN build working again

third_party/google_toolbox_for_mac/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.
 
 config("google_toolbox_for_mac_config") {
   include_dirs = [
     ".",
     "src",
     "src/AppKit",
     "src/DebugUtils",
     "src/Foundation",
   ]
+
+  # TODO(crbug.com/569158): Suppresses warnings that are treated as errors
+  # when minimum iOS version support is increased to iOS 9 and up.
+  # This should be removed once all deprecation violations have been fixed.
+  cflags = [ "-Wno-deprecated-declarations" ]

[Nico, 2016/06/22 22:53:33]

so this config is a public_config below and this has disabled deprecation
warnings for all code depending on this (e.g. the chrome target).

1. Please fix this
2. How can we make it harder for people to make catastrophic mistakes like this?
Should configs listed in public_configs have to be declared via public_config(),
so that it's visible at the config site that changing it isn't some local thing?

 }
 
 component("google_toolbox_for_mac") {
   sources = [
     "src/DebugUtils/GTMMethodCheck.h",
     "src/DebugUtils/GTMMethodCheck.m",
     "src/Foundation/GTMLightweightProxy.h",
     "src/Foundation/GTMLightweightProxy.m",
     "src/Foundation/GTMNSDictionary+URLArguments.h",
     "src/Foundation/GTMNSDictionary+URLArguments.m",
@@ skipping 171 matching lines @@
   if (is_component_build) {
     # GTM is third-party code, so we don't want to add _EXPORT
     # annotations to it, so build it without -fvisibility=hidden
     # (else the interface class symbols will be hidden in a 64bit
     # build). Only do this in a component build, so that the shipping
     # chrome binary doesn't end up with unnecessarily exported
     # symbols.
     configs -= [ "//build/config/gcc:symbol_visibility_hidden" ]
   }
 }