Revert of Ignore deprecated declaration warnings in GTM.

third_party/google_toolbox_for_mac/google_toolbox_for_mac.gyp

Index: third_party/google_toolbox_for_mac/google_toolbox_for_mac.gyp
diff --git a/third_party/google_toolbox_for_mac/google_toolbox_for_mac.gyp b/third_party/google_toolbox_for_mac/google_toolbox_for_mac.gyp
index b375725d5a76c43f401742d071b6bdcb41cb95aa..b8dea1945e3a114f4111d2ac9879e7cb9a531ebc 100644
--- a/third_party/google_toolbox_for_mac/google_toolbox_for_mac.gyp
+++ b/third_party/google_toolbox_for_mac/google_toolbox_for_mac.gyp
@@ -22,12 +22,6 @@
           'src/DebugUtils',
           'src/Foundation',
         ],
-      },
-      # GTM supports ancient iOS and OSX versions, so it's full of APIs that
-      # have been deprecated in more recent iOS and OSX versions. Ignore all
-      # deprecated-declarations warnings.
-      'xcode_settings': {
-        'WARNING_CFLAGS': ['-Wno-deprecated-declarations'],
       },
       'sources': [
         'src/AddressBook/GTMABAddressBook.h',
@@ -225,6 +219,12 @@
             ['include', '^src/Foundation/GTMStringEncoding\\.m$'],
             ['include', '^src/iPhone/'],
           ],
+          # TODO(crbug.com/569158): Suppresses warnings that are treated as
+          # errors when minimum iOS version support is increased to iOS 9. This
+          # should be removed once all deprecation violations have been fixed.
+          'xcode_settings': {
+            'WARNING_CFLAGS': ['-Wno-deprecated-declarations'],
+          },
         }],
       ],
     },