Move tsan suppression for SequencedWorkerPool to benign section

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 # running overnight and removing outdated bugs/suppressions.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 384 matching lines @@
   fun:HistogramSynchronizer::DeserializeHistogramList*
 }
 
 {
    bug_104776 Benign race to initialize pointer with the same value again.
    ThreadSanitizer:Race
    fun:base::StatisticsRecorder::FindHistogram
    fun:base::*Histogram::FactoryGet
 }
 
+{
+   bug_115987a [benign races in Histogram in SequencedWorkerPool]
+   ThreadSanitizer:Race
+   ...
+   fun:base::Histogram::*
+   fun:base::SequencedWorkerPool::*
+}
+
+# Histogram macros involve string comparison in debug mode.
+{
+   bug_115987b [benign races in Histogram in SequencedWorkerPool]
+   ThreadSanitizer:Race
+   ...
+   fun:std::operator==
+   fun:base::SequencedWorkerPool::*
+}
+
 # 3. Suppressions for real chromium bugs that are not yet fixed.
 ############################
 # Real races in Chromium
 {
   bug_23433
   ThreadSanitizer:Race
   fun:*logging*SetMinLogLevel*
 }
 
 {
@@ skipping 436 matching lines @@
 }
 {
   bug_115540
   ThreadSanitizer:Race
   fun:base::Thread::message_loop
   fun:content::BrowserThreadImpl::PostTaskHelper
   fun:content::BrowserThread::PostTask
   fun:AudioRendererHost::OnCreated
   fun:media::AudioOutputController::DoCreate
 }
-{
-   bug_115987
-   ThreadSanitizer:Race
-   ...
-   fun:base::Histogram::Add
-   fun:base::SequencedWorkerPool::Inner::GetWork
-   fun:base::SequencedWorkerPool::Inner::ThreadLoop
-}
+