Set mac_deployment_target default to 10.7

webrtc/supplement.gypi

 {
   'variables': {
     'variables': {
       'webrtc_root%': '<(DEPTH)/webrtc',
+      # Override the default (10.6) in Chromium's build/common.gypi.
+      # Needed for ARC and libc++.
+      'mac_deployment_target%': '10.7',
     },
     'webrtc_root%': '<(webrtc_root)',
+    'mac_deployment_target%': '<(mac_deployment_target)',
     'build_with_chromium': 0,
     'conditions': [
       ['OS=="ios"', {
         # Default to using BoringSSL on iOS.
         'use_openssl%': 1,
 
         # Set target_subarch for if not already set. This is needed because the
         # Chromium iOS toolchain relies on target_subarch being set.
         'conditions': [
           ['target_arch=="arm" or target_arch=="ia32"', {
@@ skipping 26 matching lines @@
             ],
             'sources': [
               '<(webrtc_root)/build/sanitizers/tsan_suppressions_webrtc.cc',
             ],
           }],
         ],
       }],
     ],
   },
 }