Use TaskRunner WorkerPool for ServerBoundCertService in TestURLRequestContext.

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 # running overnight and removing outdated bugs/suppressions.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 1826 matching lines @@
    fun:testing::internal::TestFactoryImpl::CreateTest
 }
 {
    bug_125807b
    Heapcheck:Leak
    ...
    fun:TransportSecurityPersister::TransportSecurityPersister
    fun:TransportSecurityPersisterTest::SetUp
 }
 {
-   bug_127237
-   Heapcheck:Leak
-   fun:MessageLoop::MessageLoop
-   fun:base::Thread::ThreadMain
-   fun:base::::ThreadFunc
-}
-{
    bug_127716
    Heapcheck:Leak
    fun:*Image
    fun:BrowserThemePack::LoadRawBitmapsTo
    fun:BrowserThemePack::BuildFromExtension
    fun:BrowserThemePackTest_CanBuildAndReadPack_Test::TestBody
 }
 {
    bug_127717
    Heapcheck:Leak
@@ skipping 39 matching lines @@
    Heapcheck:Leak
    fun:Pickle::Resize
    fun:Pickle::Pickle
    fun:*Message
    fun:__gnu_cxx::new_allocator::construct
    fun:std::vector::push_back
    fun:IPC::TestSink::OnMessageReceived
    fun:IPC::TestSink::Send
    fun:NaClIPCAdapter::SendMessageOnIOThread
 }