Update valgrind suppressions for mac_util::SetFileBackupExclusion leaks.

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 # running overnight and removing outdated bugs/suppressions.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 433 matching lines @@
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN11ProfileImplC2ERK8FilePath
    fun:_ZN11ProfileImplC1ERK8FilePath
    fun:_ZN7Profile13CreateProfileERK8FilePath
    fun:_ZN14ProfileManager13CreateProfileERK8FilePath
    fun:_ZN14ProfileManager10GetProfileERK8FilePath
    fun:_ZN14ProfileManager17GetDefaultProfileERK8FilePath
 }
 {
-   bug_29681
+   bug_28072
    Memcheck:Leak
    ...
    fun:CSBackupSetItemExcluded
    fun:_ZN8mac_util22SetFileBackupExclusionERK8FilePathb
    fun:_ZN7history15HistoryDatabase4InitERK8FilePathS3_
    fun:_ZN7history14HistoryBackend8InitImplEv
    fun:_ZN7history14HistoryBackend4InitEb
 }
 {
-   bug_29681
+   bug_28072
    Memcheck:Addr2
    ...
    fun:CSBackupSetItemExcluded
    fun:_ZN8mac_util22SetFileBackupExclusionERK8FilePathb
    fun:_ZN7history15HistoryDatabase4InitERK8FilePathS3_
    fun:_ZN7history14HistoryBackend8InitImplEv
    fun:_ZN7history14HistoryBackend4InitEb
 }