Compile rtc_base_objc and rtc_api_objc for Mac

webrtc/supplement.gypi

Index: webrtc/supplement.gypi
diff --git a/webrtc/supplement.gypi b/webrtc/supplement.gypi
index edccd4d81dbcc7aac9c19a87b94e03a0755fd1e6..a86affd8e63afa8849d9e9e7192d1e3c121c0f72 100644
--- a/webrtc/supplement.gypi
+++ b/webrtc/supplement.gypi
@@ -3,8 +3,8 @@
     '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',
+      # Needed for ARC, libc++, and nullability.
+      'mac_deployment_target%': '10.10',
       # Disable use of sysroot for Linux. It's enabled by default in Chromium,
       # but it currently lacks the libudev-dev package.
       # TODO(kjellander): Remove when crbug.com/561584 is fixed.
@@ -12,6 +12,8 @@
     },
     'webrtc_root%': '<(webrtc_root)',
     'mac_deployment_target%': '<(mac_deployment_target)',
+    'mac_deployment_target_major%': 10,

[kjellander_webrtc, 2016/02/03 07:57:33]

I give up and to accept these two new variables after reading your thorough
analysis - thanks for putting in the effort!

Can you add a comment here (and at mac_deployment_target above) to point out
that they need to be kept in sync?
Also mention that these latter two does not exist in Chromium.

[hjon_webrtc, 2016/02/04 01:43:03]

Done.

+    'mac_deployment_target_minor%': 10,
     'use_sysroot%': '<(use_sysroot)',
     'build_with_chromium': 0,
     'conditions': [