Suppressing memory leak in HistoryBackend::Init

tools/valgrind/memcheck/suppressions.txt

 # There are three kinds of suppressions in this file.
 # 1. third party stuff we have no control over
 #
 # 2. intentional unit test errors, or 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 (but a few aren't yet).
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 3525 matching lines @@
    Memcheck:Leak
    fun:malloc
    fun:realloc
    fun:realloc
    fun:min_heap_reserve
    fun:event_add
    fun:_ZN4base19MessagePumpLibevent3RunEPNS_11MessagePump8DelegateE
    fun:_ZN11MessageLoop11RunInternalEv
    fun:_ZN11MessageLoop10RunHandlerEv
 }
+{
+   bug_50304
+   Memcheck:Leak
+   fun:_Znw*
+   fun:_ZNSs4_Rep9_S_createEjjRKSaIcE
+   fun:_ZNSs4_Rep8_M_cloneERKSaIcEj
+   fun:_ZNSs7reserveEj
+   fun:_ZNSs6appendEjc
+   fun:_ZNK8FilePath6AppendERKSs
+   fun:_ZNK7history14HistoryBackend*FileNameEv
+   fun:_ZN7history14HistoryBackend8InitImplEv
+   fun:_ZN7history14HistoryBackend4InitEb
+   fun:_Z16DispatchToMethodIN7history14HistoryBackendEMS1_FvbEbEvPT_T0_RK6Tuple1IT1_E
+   fun:_ZN14RunnableMethodIN7history14HistoryBackendEMS1_FvbE6Tuple1IbEE3RunEv
+}