Another leak added by r74850 but the root cause is 70115.

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 # running overnight and removing outdated bugs/suppressions.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 1146 matching lines @@
    Bug_70062
    Heapcheck:Leak
    fun:PR_NewLock
    fun:InitSessionCacheLocks
    fun:initSessionCacheLocksLazily
    fun:PR_CallOnce
 }
 {
    bug_70115
    Heapcheck:Leak
+   ...
    fun:FilePathWatcher
    fun:PluginService
    fun:DefaultSingletonTraits::New
    fun:Singleton::get
    fun:PluginService::GetInstance
    fun:ResourceDispatcherHost::BeginRequest
    fun:ResourceDispatcherHost::OnRequestResource
    fun:IPC::MessageWithTuple::Dispatch
    fun:ResourceDispatcherHost::OnMessageReceived
    fun:ResourceDispatcherHostTest::MakeTestRequest
@@ skipping 58 matching lines @@
    fun:::DownloadFileTest::SetUp
 }
 {
    bug_71909
    Heapcheck:Leak
    fun:TestingProfile::CreateRequestContext
    fun:MockService
    ...
    fun:ExtensionUpdaterTest*
 }