GN: Get Mac build working for IPC target at least.

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
new file mode 100644
index 0000000000000000000000000000000000000000..b9fb530cb46611790974e1cef531c260e36b6a9b
--- /dev/null
+++ b/build/config/mac/mac_sdk.gni
@@ -0,0 +1,25 @@
+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+declare_args() {
+  # Minimum supported version of the Mac SDK.
+  mac_sdk_min = "10.6"
+
+  # Path to a specific version of the Mac SDK.

[brettw, 2014/01/08 18:43:44]

Can you document the behavior if it's left empty? I think it would also be good
to say if this needs to have a slash at the end (looks like not).

[bbudge, 2014/01/08 20:22:55]

Done.

+  mac_sdk_path = ""
+}
+
+if (is_chrome_branded && is_official_build) {
+  find_sdk_args = ["--verify", mac_sdk_min "--sdk_path=" + mac_sdk_path]

[brettw, 2014/01/08 18:43:44]

Can you put spaces inside the [] here and below (but not for the "[0]")? I've
been doing that.

+} else {
+  find_sdk_args = [mac_sdk_min]
+}
+# Use "list lines" and take the first to get version string without a newline.
+find_sdk_lines =
+    exec_script("//build/mac/find_sdk.py", find_sdk_args, "list lines")
+mac_sdk_version = find_sdk_lines[0]
+if (mac_sdk_path == "") {
+  mac_sdk_root = "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX"
+  mac_sdk_path = mac_sdk_root + mac_sdk_version + ".sdk"
+}