Fix the //sandbox/mac build when using a modern (10.7+) SDK.

sandbox/mac/sandbox_mac.gypi

Index: sandbox/mac/sandbox_mac.gypi
diff --git a/sandbox/mac/sandbox_mac.gypi b/sandbox/mac/sandbox_mac.gypi
index 29a65342b6c435886596e9522c270e0f613c3aa3..a2a616fcfb3df8ebe64747037e089c9dc46ed36d 100644
--- a/sandbox/mac/sandbox_mac.gypi
+++ b/sandbox/mac/sandbox_mac.gypi
@@ -41,43 +41,51 @@
           '$(SDKROOT)/usr/lib/libbsm.dylib',
         ],
       },
-      'actions': [
-        {
-          'variables': {
-            'generate_stubs_script': '../tools/generate_stubs/generate_stubs.py',
-            'generate_stubs_header_path': 'xpc_stubs_header.fragment',
-            'generate_stubs_sig_public_path': 'xpc_stubs.sig',
-            'generate_stubs_sig_private_path': 'xpc_private_stubs.sig',
-            'generate_stubs_project': 'sandbox/mac',
-            'generate_stubs_output_stem': 'xpc_stubs',
-          },
-          'action_name': 'generate_stubs',
-          'inputs': [
-            '<(generate_stubs_script)',
-            '<(generate_stubs_header_path)',
-            '<(generate_stubs_sig_public_path)',
-            '<(generate_stubs_sig_private_path)',
+      'conditions': [
+        # When the build SDK is 10.6, generate a dynamic stub loader. When the
+        # SDK is higher, then libxpc.dylib will be loaded automatically as part
+        # of libSystem, and only forward declarations of private symbols are
+        # necessary.
+        ['mac_sdk == "10.6"', {
+          'actions': [
+            {
+              'variables': {
+                'generate_stubs_script': '../tools/generate_stubs/generate_stubs.py',
+                'generate_stubs_header_path': 'xpc_stubs_header.fragment',
+                'generate_stubs_sig_public_path': 'xpc_stubs.sig',
+                'generate_stubs_sig_private_path': 'xpc_private_stubs.sig',
+                'generate_stubs_project': 'sandbox/mac',
+                'generate_stubs_output_stem': 'xpc_stubs',
+              },
+              'action_name': 'generate_stubs',
+              'inputs': [
+                '<(generate_stubs_script)',
+                '<(generate_stubs_header_path)',
+                '<(generate_stubs_sig_public_path)',
+                '<(generate_stubs_sig_private_path)',
+              ],
+              'outputs': [
+                '<(INTERMEDIATE_DIR)/<(generate_stubs_output_stem).cc',
+                '<(SHARED_INTERMEDIATE_DIR)/<(generate_stubs_project)/<(generate_stubs_output_stem).h',
+              ],
+              'action': [
+                'python',
+                '<(generate_stubs_script)',
+                '-i', '<(INTERMEDIATE_DIR)',
+                '-o', '<(SHARED_INTERMEDIATE_DIR)/<(generate_stubs_project)',
+                '-t', 'posix_stubs',
+                '-e', '<(generate_stubs_header_path)',
+                '-s', '<(generate_stubs_output_stem)',
+                '-p', '<(generate_stubs_project)',
+                '-x', 'SANDBOX_EXPORT',
+                '<(generate_stubs_sig_public_path)',
+                '<(generate_stubs_sig_private_path)',
+              ],
+              'process_outputs_as_sources': 1,
+              'message': 'Generating XPC stubs for 10.6 compatability.',
+            },
           ],
-          'outputs': [
-            '<(INTERMEDIATE_DIR)/<(generate_stubs_output_stem).cc',
-            '<(SHARED_INTERMEDIATE_DIR)/<(generate_stubs_project)/<(generate_stubs_output_stem).h',
-          ],
-          'action': [
-            'python',
-            '<(generate_stubs_script)',
-            '-i', '<(INTERMEDIATE_DIR)',
-            '-o', '<(SHARED_INTERMEDIATE_DIR)/<(generate_stubs_project)',
-            '-t', 'posix_stubs',
-            '-e', '<(generate_stubs_header_path)',
-            '-s', '<(generate_stubs_output_stem)',
-            '-p', '<(generate_stubs_project)',
-            '-x', 'SANDBOX_EXPORT',
-            '<(generate_stubs_sig_public_path)',
-            '<(generate_stubs_sig_private_path)',
-          ],
-          'process_outputs_as_sources': 1,
-          'message': 'Generating XPC stubs for 10.6 compatability.',
-        },
+        }],
       ],
     },
     {