Bump mac_sdk to 10.8

tools/gyp/xcode.gypi

Index: tools/gyp/xcode.gypi
diff --git a/tools/gyp/xcode.gypi b/tools/gyp/xcode.gypi
index 335500ac022b9742653ce1058d6430fee8dcc625..1799baf04456d7959533c005c807f260942d9143 100644
--- a/tools/gyp/xcode.gypi
+++ b/tools/gyp/xcode.gypi
@@ -18,8 +18,8 @@
     # Chrome normally builds with the Mac OS X 10.5 SDK and sets the
     # deployment target to 10.5.  Other projects, such as O3D, may override
     # these defaults.
-    'mac_sdk%': '<!(python <(DEPTH)/tools/gyp/find_mac_sdk.py 10.7)',
-    'mac_deployment_target%': '10.7',
+    'mac_sdk%': '<!(python <(DEPTH)/tools/gyp/find_mac_sdk.py 10.8)',
+    'mac_deployment_target%': '10.8',
   },
   'xcode_settings': {
     # DON'T ADD ANYTHING NEW TO THIS BLOCK UNLESS YOU REALLY REALLY NEED IT!