TSAN: Suppress a race in PrintJobTest.SimplePrint.

tools/valgrind/tsan/suppressions.txt

 # There are a few 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 # running overnight and removing outdated bugs/suppressions.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 1148 matching lines @@
   fun:remoting::Me2MeNativeMessagingHost::ProcessMessage
   fun:base::internal::RunnableAdapter::Run
 }
 {
   bug_330903
   ThreadSanitizer:Race
   fun:gcm::GCMClientMock::SetIsLoading
   fun:gcm::GCMProfileServiceRegisterTest_GCMClientLoadingCompletedAfterReadingRegistration_Test::TestBody
   fun:testing::internal::HandleSehExceptionsInMethodIfSupported
 }
+{
+  bug_344704
+  ThreadSanitizer:Race
+  fun:base::Thread::message_loop
+  fun:printing::PrintJob::UpdatePrintedDocument
+  fun:printing::PrintJob::ControlledWorkerShutdown
+  fun:printing::PrintJob::Stop
+  fun:PrintJobTest_SimplePrint_Test::TestBody
+}