[Mac] Add testing code to expose an NSColor memory leak.

tools/valgrind/memcheck/suppressions_mac.txt

 # There are three kinds of suppressions in this file:
 # 1. Third party stuff we have no control over.
 #
 # 2. Intentional unit test errors, 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.
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 655 matching lines @@
    fun:mallocWithAlarm
    ...
    fun:_ZN7history16ArchivedDatabase4InitERK8FilePath
 }
 {
    bug_20997
    Memcheck:Param
    socketcall.sendmsg(msg.msg_iov[i])
    fun:sendmsg$UNIX2003
    fun:_ZN3IPC7Channel11ChannelImpl4SendEPNS_7MessageE
+} 
+{
+  bug_21137
+  Memcheck:Leak
+  fun:malloc
+  ...
+  fun:+[NSColor keyboardFocusIndicatorColor]
+  ...
+  fun:-[AutocompleteTextFieldCell drawWithFrame:inView:]
 }