Allow WebRTC to require Mac 10.7 deployments in GN builds.

build/config/mac/mac_sdk.gni

Index: build/config/mac/mac_sdk.gni
diff --git a/build/config/mac/mac_sdk.gni b/build/config/mac/mac_sdk.gni
index 8767aa4108b85a10780e1795aad7e88df0a1104d..23e2d83af94c59ca42bcc698f0e037c2a0dcd078 100644
--- a/build/config/mac/mac_sdk.gni
+++ b/build/config/mac/mac_sdk.gni
@@ -4,12 +4,17 @@
 
 import("//build/config/chrome_build.gni")
 
+# See https://bugs.chromium.org/p/webrtc/issues/detail?id=5453.
+# We can drop the rtc_require_mac_10_7_deployment flag when Chromium

[Nico, 2016/04/04 18:01:22]

rtc_require_mac_10_7_deployment isn't referenced by anything but this comment.

we're about to bump the deployment target to 10.7 here
https://codereview.chromium.org/1847533004/ and will bump it to 10.9 soon. is
this build_overrides file still needed then? does webrtc keep targeting older os
x versions once chromium stops doing so?

[tkchin_webrtc, 2016/04/04 18:49:01]

We haven't done the work on WebRTC side to fix GN builds for iOS/Mac yet. But
this override is needed to do so (we're using the GYP equivalent).

Afaik there is no reason for us to continue to target old deployment targets if
Chromium is not doing so. I would like very much to be targeting 10.9.

+# also requires a 10.7 deployment target.
+import("//build_overrides/build.gni")
+
 declare_args() {
   # Minimum supported version of the Mac SDK.
   mac_sdk_min = "10.10"
 
   # Minimum supported version of OSX.
-  mac_deployment_target = "10.6"
+  mac_deployment_target = mac_deployment_target_build_override
 
   # Path to a specific version of the Mac SDK, not including a backslash at
   # the end. If empty, the path to the lowest version greater than or equal to