Fix BrowserAccessibilityManager valgrind errors.

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 # running overnight and removing outdated bugs/suppressions.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 1013 matching lines @@
    Memcheck:Addr4
    ...
    fun:FSFindFolder
    fun:_ZN12_GLOBAL__N_124GetPluginCommonDirectoryEPSt6vectorI8FilePathSaIS1_EEb
    fun:_ZN6webkit5npapi10PluginList20GetPluginDirectoriesEPSt6vectorI8FilePathSaIS2_EE
    fun:_ZN6webkit5npapi10PluginList11LoadPluginsEb
    fun:_ZN6webkit5npapi10PluginList10GetPluginsEbPSt6vectorI13WebPluginInfoSaIS2_EE
    fun:_ZN13PluginUpdater30GetPreferencesDataOnFileThreadEPv
 }
 {
-   bug_59243_a
-   Memcheck:Leak
-   fun:_Znw*
-   fun:_ZN20BrowserAccessibility6CreateEv
-   fun:_ZN24BrowserAccessibilityTest5SetUpEv
-}
-{
-   bug_59243_b
-   Memcheck:Leak
-   fun:_Znw*
-   ...
-   fun:_ZNSt3mapIiSbItN4base20string16_char_traitsESaItEESt4lessIiESaISt4pairIKiS3_EEEaSERKSA_
-   fun:_ZN20BrowserAccessibility10InitializeEP27BrowserAccessibilityManagerPS_iiRKN11webkit_glue16WebAccessibilityE
-   fun:_ZN24BrowserAccessibilityTest5SetUpEv
-}
-{
    bug_51682a
    Memcheck:Leak
    fun:malloc
    fun:__cxa_get_globals
    fun:__cxa_allocate_exception
    fun:_ZN8Security9CssmError7throwMeEi
    fun:_ZN9RSASigner6verifyEPKvmS1_m
    fun:_ZN16SignatureContext5finalERKN8Security8CssmDataE
    fun:_ZL20cssm_VerifyDataFinallyPK9cssm_data
    fun:CSSM_VerifyDataFinal
@@ skipping 784 matching lines @@
    Memcheck:Addr1
    fun:IOCFUnserializeparse
    fun:IOCFUnserialize
    fun:IORegistryEntryCreateCFProperties
    fun:_ZN15CVCGDisplayLink17setCurrentDisplayEj
    fun:_ZN15CVCGDisplayLink18initWithCGDisplaysEPjlPi
    fun:CVDisplayLinkCreateWithCGDisplays
    fun:CVDisplayLinkCreateWithActiveCGDisplays
    fun:-[AcceleratedPluginView initWithRenderWidgetHostViewMac:pluginHandle:]
 }