Add base/md5* to ThreadSanitizer ignore list.

tools/valgrind/tsan/ignores.txt

 # This file lists the functions, object files and source files
 # which should be ignored (i.e. not instrumented) by ThreadSanitizer.
 # See http://code.google.com/p/data-race-test/wiki/ThreadSanitizerIgnores.
 
 # ignore these libraries
 obj:*/libfreetype*
 obj:*/libdbus*
 
 # we ignore the whole NSS library for now since
 # its instrumentation is very slow.
@@ skipping 47 matching lines @@
 src:*base/synchronization/lock*
 src:*base/synchronization/waitable_event*
 
 # Don't instrument code dealing with atomics (base::subtle)
 fun:*base*subtle*Release_Store*
 fun:*base*subtle*NoBarrier_CompareAndSwap*
 fun:*base*subtle*NoBarrier_Load*
 # Keep some mangling so we don't match NoBarrier_AtomicIncrement
 fun:*base*subtle23Barrier_AtomicIncrement*
 
+# MD5 computations are very slow due since sums are computed by
+# repeatedly calling tiny functions and is unlikely to race with
+# anything.
+src:*base/md5*
+
 # Don't instrument tcmalloc
 src:*/tcmalloc/*
 
 # This function is heavy in net_unittests
 fun_r:*disk_cache*BackendImpl*CheckAllEntries*
 
 # V8 is a hot-spot under ThreadSanitizer.
 # Lots of tiny functions there...
 # TODO(timurrrr):
 # Can we miss data races on V8 objects due to non thread-safe API calls
@@ skipping 75 matching lines @@
 fun:__gen_tempname
 
 # The sqlite cache is racing against a few different stacktraces,
 # so let's ignore it recursively. See http://crbug.com/84094
 fun_r:pcache1Fetch
 
 # "Suppress" a data race in TraceLog::GetCategory which has
 # fun:MessageLoop::RunTask at the top of the "current" stack which we don't want
 # to suppress. See http://crbug.com/98926
 fun:*base*debug*TraceLog*GetCategoryInternal*