Mark SessionHistoryTest.FrameBackForward flaky on Mac.

BUG=61619

Review URL: http://codereview.chromium.org/8555005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@109869 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/session_history_uitest.cc

@@ -146,7 +146,7 @@ TEST_F(SessionHistoryTest, MAYBE_BasicBackForward) {
   EXPECT_EQ(L"bot3", GetTabTitle());
 }
 
-#if defined(OS_WIN)
+#if defined(OS_WIN) || defined(OS_MAC)
 // See http://crbug.com/61619
 #define MAYBE_FrameBackForward FLAKY_FrameBackForward
 #else