Valgrind Mac: Put a suppression back in for a sporatic leak.

tools/valgrind/memcheck/suppressions_mac.txt

 # There are three kinds of suppressions in this file:
 # 1. Third party stuff we have no control over.
 #
 # 2. Intentional unit test errors, stuff that is somehow a false positive
 # in our own code, or stuff that is so trivial it's not worth fixing.
 #
 # 3. Suppressions for real chromium bugs that are not yet fixed.
 # These should all be in chromium's bug tracking system.
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 378 matching lines @@
 {
    bug_28072c
    Memcheck:Addr2
    ...
    fun:CSBackupSetItemExcluded
    fun:_ZN8mac_util22SetFileBackupExclusionERK8FilePathb
    fun:_ZN7history15HistoryDatabase4InitERK8FilePathS3_
    fun:_ZN7history14HistoryBackend8InitImplEv
    fun:_ZN7history14HistoryBackend4InitEb
 }
+# Note: bug 31634 happens very sporatically.
+{
+   bug_31634
+   Memcheck:Leak
+   fun:malloc_zone_malloc
+   fun:_CFRuntimeCreateInstance
+   fun:__CFDictionaryInit
+   fun:CFDictionaryCreate
+   fun:classDescription
+}
 {
    bug_35164
    Memcheck:Cond
    ...
    fun:gl_context_init_client_state
    fun:ogl_begin_rendering
    fun:CARenderOGLRender
    fun:view_draw
 }
 {
@@ skipping 1191 matching lines @@
    fun:_HandlePopUpMenuSelection7
    fun:_NSPopUpCarbonMenu3
    fun:_NSPopUpCarbonMenu2
    fun:_NSPopUpCarbonMenu1
    fun:-[NSCarbonMenuImpl _popUpContextMenu:withEvent:forView:withFont:]
    fun:-[NSMenu _popUpContextMenu:withEvent:forView:withFont:]
    fun:-[NSMenu _popUpContextMenu:withEvent:forView:]
    fun:-[ProfileMenuButton mouseDown:]
    fun:_ZN35ProfileMenuButtonTest_MenuTest_Test8TestBodyEv
 }