Disable extension startup tests on Mac, since they're causing it to hang.

chrome/test/startup/startup_test.cc

Index: chrome/test/startup/startup_test.cc
diff --git a/chrome/test/startup/startup_test.cc b/chrome/test/startup/startup_test.cc
index eac8173b5569b0b61264e45bc62d2dd6edd10a76..69035d828351b23849e9c1efc7265f0f2001d0d4 100644
--- a/chrome/test/startup/startup_test.cc
+++ b/chrome/test/startup/startup_test.cc
@@ -160,6 +160,11 @@ TEST_F(StartupTest, PerfCold) {
                  UITest::DEFAULT_THEME);
 }
 
+#if defined(OS_MACOSX)
+// TODO(mpcomplete): running these tests on a mac builder results in leaked
+// chrome processes, causing the build slave to hang.
+// http://code.google.com/p/chromium/issues/detail?id=22287
+#else
 TEST_F(StartupTest, PerfExtensionEmpty) {
   SetUpWithFileURL();
   SetUpWithExtensionsProfile("empty");
@@ -198,7 +203,7 @@ TEST_F(StartupTest, PerfExtensionContentScript50) {
                  false /* cold */, false /* not important */,
                  UITest::DEFAULT_THEME);
 }
-
+#endif
 
 #if defined(OS_WIN)
 // TODO(port): Enable gears tests on linux/mac once gears is working.