Cancel unused timeout events. Without this change they can...

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 # running overnight and removing outdated bugs/suppressions.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 224 matching lines @@
    bug_17576
    Memcheck:Leak
    ...
    fun:findLockInfo
    ...
    fun:unixOpen
    ...
    fun:openDatabase
 }
 {
-   libevent does not provide a way to clean up unused oneshot timers at exit
-   Memcheck:Leak
-   fun:calloc
-   fun:event_base_once
-   fun:event_base_loopexit
-   fun:_ZN4base19MessagePumpLibevent3RunEPNS_11MessagePump8DelegateE
-}
-{
    # array of weak references freed but not processed?
    bug_16576
    Memcheck:Leak
    ...
    fun:g_object_weak_ref
    fun:g_object_add_weak_pointer
 }
 {
    bug_16161
    Memcheck:Leak
@@ skipping 803 matching lines @@
    fun:_Z10cssyyparsePv
    fun:_ZN7WebCore9CSSParser10parseSheetEPNS_13CSSStyleSheetERKNS_6StringE
 }
 {
    bug_26216
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN9Extension25LoadExtensionActionHelperEPK15DictionaryValuePSs
    fun:_ZN39ExtensionTest_LoadPageActionHelper_Test8TestBodyEv
 }