suppress memory leak from MetricsLog::MetricsLog

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 # running overnight and removing outdated bugs/suppressions.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 6520 matching lines @@
    ...
    fun:_ZN18ValueStoreFrontend*
 }
 {
     bug_175985
     Memcheck:Uninitialized
     fun:_ZN2cc13LayerTreeHost13setDebugStateERKNS_19LayerTreeDebugStateE
     ...
     fun:_ZN6WebKit20WebLayerTreeViewImpl*
 }
+{
+   bug_176048
+   Memcheck:Leak
+   fun:_Znw*
+   fun:_ZN4base8internal20PostTaskAndReplyImpl16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIFvvEEESA_
+   fun:_ZN4base10TaskRunner16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIFvvEEES9_
+   fun:_ZN22MetricsNetworkObserver25ProbeWifiPHYLayerProtocolEv
+   fun:_ZN22MetricsNetworkObserverC1Ev
+   fun:_ZN10MetricsLogC2ERKSsi
+   fun:_ZN12_GLOBAL__N_114TestMetricsLogC1ERKSsi
+}