Add the stack signature of a small memory leak found in SessionHistoryTest.Hi...

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 # running overnight and removing outdated bugs/suppressions.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 1301 matching lines @@
    fun:_Znwj
    fun:_ZN7WebCore26PlatformMessagePortChannel19postMessageToRemoteEN3WTF10PassOwnPtrINS_18MessagePortChannel9EventDataEEE
    fun:_ZN7WebCore18MessagePortChannel19postMessageToRemoteEN3WTF10PassOwnPtrINS0_9EventDataEEE
    fun:_ZN7WebCore11MessagePort11postMessageERKNS_6StringEPKN3WTF6VectorINS4_6RefPtrIS0_EELj1EEERi
    fun:_ZN7WebCore8V8Custom32v8MessagePortPostMessageCallbackERKN2v89ArgumentsE
    fun:_ZN2v88internal21Builtin_HandleApiCallENS0_9ArgumentsE
    ...
    fun:_ZN2v88internal6InvokeEbNS0_6HandleINS0_10JSFunctionEEENS1_INS0_6ObjectEEEiPPPS4_Pb
    fun:_ZN2v88internal9Execution4CallENS0_6HandleINS0_10JSFunctionEEENS2_INS0_6ObjectEEEiPPPS5_Pb
 }
+{
+   bug_22984
+   Memcheck:Leak
+   fun:_Znwj
+   fun:_ZN27ScopedRunnableMethodFactoryI12SpellCheckerE17NewRunnableMethodIMS0_FvvEEEP4TaskT_
+   fun:_ZN12SpellChecker18OnURLFetchCompleteEPK10URLFetcherRK4GURLRK16URLRequestStatusiRKSt6vectorISsSaISsEERKSs
+   fun:_ZN10URLFetcher4Core21OnCompletedURLRequestERK16URLRequestStatus
+   fun:_Z16DispatchToMethodIN10URLFetcher4CoreEMS1_FvRK16URLRequestStatusES2_EvPT_T0_RK6Tuple1IT1_E
+   fun:_ZN14RunnableMethodIN10URLFetcher4CoreEMS1_FvRK16URLRequestStatusE6Tuple1IS2_EE3RunEv
+   fun:_ZN11MessageLoop7RunTaskEP4Task
+   fun:_ZN11MessageLoop21DeferOrRunPendingTaskERKNS_11PendingTaskE
+   fun:_ZN11MessageLoop6DoWorkEv
+   fun:_ZN4base19MessagePumpLibevent3RunEPNS_11MessagePump8DelegateE
+   fun:_ZN11MessageLoop11RunInternalEv
+   fun:_ZN11MessageLoop10RunHandlerEv
+   fun:_ZN11MessageLoop3RunEv
+   fun:_ZN4base6Thread3RunEP11MessageLoop
+   fun:_ZN4base6Thread10ThreadMainEv
+   fun:_Z10ThreadFuncPv
+   fun:start_thread
+   fun:clone
+}