Disable BubbleCreationTypesTest on Windows and Chrome OS.

ash/common/system/tray/system_tray_unittest.cc

Index: ash/common/system/tray/system_tray_unittest.cc
diff --git a/ash/common/system/tray/system_tray_unittest.cc b/ash/common/system/tray/system_tray_unittest.cc
index abc9d053506c48121dbf81babc8aa9283ea61b75..4a9dcc0fbae9e8e36d538e7191f1e1eff68cd268 100644
--- a/ash/common/system/tray/system_tray_unittest.cc
+++ b/ash/common/system/tray/system_tray_unittest.cc
@@ -357,7 +357,13 @@ TEST_F(SystemTrayTest, SystemTrayNotifications) {
   ASSERT_TRUE(test_item->notification_view() != NULL);
 }
 
-TEST_F(SystemTrayTest, BubbleCreationTypesTest) {
+// Test is flaky on Win7 and Cros (crbug.com/637978).
+#if defined(OS_CHROMEOS) || defined(OS_WIN)
+#define MAYBE_BubbleCreationTypesTest DISABLED_BubbleCreationTypesTest
+#else
+#define MAYBE_BubbleCreationTypesTest BubbleCreationTypesTest
+#endif
+TEST_F(SystemTrayTest, MAYBE_BubbleCreationTypesTest) {
   SystemTray* tray = GetPrimarySystemTray();
   ASSERT_TRUE(tray->GetWidget());