Disables MultiProcessNotificationTests.

This change just disables MultiProcessNotificationTests added by r71418 <http://crrev.com/71418> because they always crash on the "Chromium Mac (valgrind)" bot. (We also disable other MultiProcessNotificationTests?)

TBR=dmaclach,thestig,timurrrr
BUG=69641
TEST=make the "Chromium Mac (valgrind)" bot green.
Review URL: http://codereview.chromium.org/6321004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@71423 0039d316-1c4b-4281-b951-d872f2087c98

tools/valgrind/gtest_exclude/unit_tests.gtest_mac.txt

@@ -19,3 +19,8 @@ PrefsControllerTest.GetPrefsViewForPage
 PrefsControllerTest.GetToolbarItemForPage
 PrefsControllerTest.ShowAndClose
 PrefsControllerTest.SwitchToPage
+
+# MultiProcessNotificationTests crash on the valgrind bot.
+# See http://crbug.com/69641.
+MultiProcessNotificationTest.BasicCreationTest
+MultiProcessNotificationTest.PostInProcessNotification