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..d32e69e362143811af5b42abbf77dffa620d27e3 100644
--- a/build/config/mac/mac_sdk.gni
+++ b/build/config/mac/mac_sdk.gni
@@ -4,12 +4,21 @@
 
 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
+# also requires a 10.7 deployment target.
+import("//build_overrides/webrtc.gni")

[brettw, 2016/02/16 22:46:46]

We're trying to make the build directory independent of any other directory.
You'll notice that the current //build directory has no references to
//build_overrides/*.

The //build directory is mirrored in
https://chromium.googlesource.com/chromium/src/build/
and can be DEPSed in by other projects (e.g. standalone V8, NaCl). However, the
//build_overrides directory is necessarily different for each such project. This
change will force each project to defined a file in their repository
"webrtc.gni" with this variable set, which I don't think we want.

This mac_deployment_target is already exposed as a build variable. Can you just
configure your bot to set it?

+
 declare_args() {
   # Minimum supported version of the Mac SDK.
   mac_sdk_min = "10.10"
 
   # Minimum supported version of OSX.
-  mac_deployment_target = "10.6"
+  if (rtc_require_mac_10_7_deployment) {
+    mac_deployment_target = "10.7"
+  } else {
+    mac_deployment_target = "10.6"
+  }
 
   # 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