Disable 2 flaky content_browsertests on Mac.

content/browser/frame_host/frame_tree_browsertest.cc

Index: content/browser/frame_host/frame_tree_browsertest.cc
diff --git a/content/browser/frame_host/frame_tree_browsertest.cc b/content/browser/frame_host/frame_tree_browsertest.cc
index e0d790fdb06c0e277e4420ec3356ded1494fef2b..5a0c453b9e7a5963f8607d537affd124a9f3f9a8 100644
--- a/content/browser/frame_host/frame_tree_browsertest.cc
+++ b/content/browser/frame_host/frame_tree_browsertest.cc
@@ -139,7 +139,13 @@ IN_PROC_BROWSER_TEST_F(FrameTreeBrowserTest, FrameTreeAfterCrash) {
 
 // Test that we can navigate away if the previous renderer doesn't clean up its
 // child frames.
-IN_PROC_BROWSER_TEST_F(FrameTreeBrowserTest, NavigateWithLeftoverFrames) {
+// Flaky on Mac. http://crbug.com/452018
+#if defined(OS_MACOSX)
+#define MAYBE_NavigateWithLeftoverFrames DISABLED_NavigateWithLeftoverFrames
+#else
+#define MAYBE_NavigateWithLeftoverFrames NavigateWithLeftoverFrames
+#endif
+IN_PROC_BROWSER_TEST_F(FrameTreeBrowserTest, MAYBE_NavigateWithLeftoverFrames) {
   GURL base_url = embedded_test_server()->GetURL("A.com", "/site_isolation/");
 
   NavigateToURL(shell(),