Widen suppressions for misunderstood atomics.

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 # running overnight and removing outdated bugs/suppressions.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 1064 matching lines @@
   ThreadSanitizer:Race
   fun:setlocale
   ...
   fun:gfx::GtkInitFromCommandLine
 }
 {
   bug_239350
   ThreadSanitizer:Race
   fun:av_buffer_unref
   fun:av_frame_unref
-  fun:avcodec_decode_video2
   ...
-  fun:media::FFmpegVideoDecoder::Decode
 }
 {
   bug_256792
   ThreadSanitizer:Race
   fun:media::AudioManagerLinux::~AudioManagerLinux
   fun:content::MockAudioManager::~MockAudioManager
   fun:content::MockAudioManager::~MockAudioManager
   fun:base::DefaultDeleter*
   fun:base::internal::scoped_ptr_impl::~scoped_ptr_impl
   fun:scoped_ptr::~scoped_ptr
@@ skipping 24 matching lines @@
 }
 {
   bug_268924
   ThreadSanitizer:Race
   fun:base::PowerMonitor::PowerMonitor
   fun:content::ChildThread::Init
   fun:content::ChildThread::ChildThread
   fun:content::UtilityThreadImpl::UtilityThreadImpl
   fun:content::UtilityMainThread::InitInternal
 }
+