Suppress one more data race in test_shell on WeakReference

tools/valgrind/tsan/suppressions.txt

 ############################
 # Chromium
 
 {
   bug_21259
   ThreadSanitizer:Race
   ...
   fun:*tracked_objects*ThreadData*StartTracking*
 }
 
@@ skipping 36 matching lines @@
   fun:*logging*SetMinLogLevel*
 }
 
 {
   bug_24419
   ThreadSanitizer:Race
   fun:*BrowserProcessImpl*nspector*iles*
 }
 
 {
-  bug_24715
+  bug_24715 (1)
   ThreadSanitizer:Race
   fun:*base*internal*WeakReference*
   ...
   fun:*AppCacheUpdateJobTest*
 }
 
 {
+  bug_24715 (2)
+  ThreadSanitizer:Race
+  fun:*base*internal*WeakReference*
+  ...
+  fun:*AppCacheResponseTest*
+}
+
+{
   bug_25385
   ThreadSanitizer:Race
   ...
   fun:*base*ThreadD*E*
 }
 
 {
   bug_25915
   ThreadSanitizer:Race
   fun:*browser_sync*BookmarkModelWorker*
@@ skipping 150 matching lines @@
   fun:tzset*
 }
 
 # Benign race in thread-safe function
 {
   fun:mkstemp*
   ThreadSanitizer:Race
   ...
   fun:mkstemp*
 }