suppress memory leak from MetricsLog::MetricsLog

tools/heapcheck/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 # running overnight and removing outdated bugs/suppressions.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 1767 matching lines @@
    fun:ThemeServiceFactory::BuildServiceInstanceFor
    fun:ProfileKeyedServiceFactory::GetServiceForProfile
    fun:ProfileKeyedServiceFactory::CreateServiceNow
    fun:ProfileDependencyManager::CreateProfileServices
    fun:TestingProfile::Init
    fun:TestingProfile::TestingProfile
    fun:OAuth2RevocationFetcherTest::OAuth2RevocationFetcherTest
    fun:OAuth2RevocationFetcherTest_RequestFailure_Test::OAuth2RevocationFetcherTest_RequestFailure_Test
    fun:testing::internal::TestFactoryImpl::CreateTest
 }
+{
+   bug_176048
+   Heapcheck:Leak
+   ...
+   fun:MetricsNetworkObserver::ProbeWifiPHYLayerProtocol
+   fun:MetricsNetworkObserver::MetricsNetworkObserver
+   fun:MetricsLog::MetricsLog
+   fun:TestMetricsLog
+}