Add tsan suppression for gamepad unittest code

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 # running overnight and removing outdated bugs/suppressions.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 374 matching lines @@
   fun:base::Histogram::*
   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
 }
+{
+  Test to detect read contention & benign race

[dhollowa, 2011/11/22 21:24:00]

There should be a bug logged to track this, then "bug_123456" added to this
suppression.

+  ThreadSanitizer:Race
+  ...
+  fun:::MockDataFetcher::GetGamepadData
+  fun:gamepad::Provider::DoPoll
+}
 
 # 3. Suppressions for real chromium bugs that are not yet fixed.
 ############################
 # Real races in Chromium
 {
   bug_23433
   ThreadSanitizer:Race
   fun:*logging*SetMinLogLevel*
 }
 
@@ skipping 268 matching lines @@
 {
    bug_104769
    ThreadSanitizer:Race
    fun:timeout_correct
    fun:event_base_loop
    fun:base::MessagePumpLibevent::Run
    fun:MessageLoop::RunInternal
    fun:MessageLoop::RunHandler
    fun:MessageLoop::Run
 }