Roll chromium_revision 7542f07..38664e7 (377632:377790) + set SDK 10.11 on Mac

webrtc/supplement.gypi

 {
   'variables': {
     'variables': {
       'webrtc_root%': '<(DEPTH)/webrtc',
-      # Override the default (10.6) in Chromium's build/common.gypi.
+      # Override the defaults in Chromium's build/common.gypi.
       # Needed for ARC and libc++.
+      'mac_sdk_min%': '10.11',
       'mac_deployment_target%': '10.7',
     },
     'webrtc_root%': '<(webrtc_root)',
     'mac_deployment_target%': '<(mac_deployment_target)',
     'use_sysroot%': '<(use_sysroot)',
     'build_with_chromium': 0,
     'conditions': [
       ['OS=="ios"', {
         # Default to using BoringSSL on iOS.
         'use_openssl%': 1,
@@ skipping 31 matching lines @@
             ],
             'sources': [
               '<(webrtc_root)/build/sanitizers/tsan_suppressions_webrtc.cc',
             ],
           }],
         ],
       }],
     ],
   },
 }