Disable TabStripModelTest.FastShutdown on Mac 64.

BUG=302156
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/25756003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226507 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/ui/tabs/tab_strip_model_unittest.cc

@@ -1709,8 +1709,9 @@ TEST_F(TabStripModelTest, NavigationForgettingDoesntAffectNewTab) {
   strip.CloseAllTabs();
 }
 
-// This fails on linux when run with the rest of unit_tests (crbug.com/302156).
-#if defined(OS_LINUX)
+// This fails on Linux when run with the rest of unit_tests (crbug.com/302156)
+// and fails consistently on Mac 64.
+#if defined(OS_LINUX) || (defined(OS_MACOSX) && ARCH_CPU_64_BITS)
 #define MAYBE_FastShutdown \
     DISABLED_FastShutdown
 #else