Fix leak in MetricsLogTest.InitialLogStabilityMetrics test.

tools/valgrind/memcheck/suppressions.txt

 # There are four 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 # running overnight and removing outdated bugs/suppressions.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 6273 matching lines @@
 {
    bug_327672
    Memcheck:Uninitialized
    fun:_ZNK7WebCore18StyleSheetContents11isCacheableEv
    fun:_ZN7WebCore9LinkStyle16setCSSStyleSheetERKN3WTF6StringERKNS_4KURLES4_PKNS_21CSSStyleSheetResourceE
    fun:_ZN7WebCore21CSSStyleSheetResource11checkNotifyEv
    ...
    fun:_ZN11webkit_glue16WebURLLoaderImpl7Context18OnCompletedRequestEibRKSsRKN4base9TimeTicksE
 }
 {
-   bug_328987
-   Memcheck:Leak
-   fun:_Znw*
-   fun:_ZN4base8internal20PostTaskAndReplyImpl16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIFvvEEESA_
-   fun:_ZN4base10TaskRunner16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIFvvEEES9_
-   fun:_ZN4base26PostTaskAndReplyWithResultIN3net20WifiPHYLayerProtocolES2_EEbPNS_10TaskRunnerERKN15tracked_objects8LocationERKNS_8CallbackIFT_vEEERKNS9_IFvT0_EEE
-   fun:_ZN22MetricsNetworkObserver25ProbeWifiPHYLayerProtocolEv
-   fun:_ZN22MetricsNetworkObserverC1Ev
-   fun:_ZN10MetricsLogC1ERKSsi
-}
-{
    bug_329104
    Memcheck:Leak
    fun:malloc
    fun:PORT_Alloc_Util
    fun:PK11_AddSlotToList
    fun:PK11_GetAllSlotsForCert
    fun:_ZNK3net24NSSProfileFilterChromeOS13IsCertAllowedERK13scoped_refptrINS_15X509CertificateEE
    fun:_ZNK3net24NSSProfileFilterChromeOS33CertNotAllowedForProfilePredicateclERK13scoped_refptrINS_15X509CertificateEE
 }