Delete callbacks after use in canned browsing data helpers.

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 # running overnight and removing outdated bugs/suppressions.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 1429 matching lines @@
    fun:_ZN7testing8internal15TestFactoryImplI40DownloadManagerTest_GetSafeFilename_TestE10CreateTestEv
 }
 {
    bug_49268_3
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN19DownloadManagerTestC2Ev
    fun:_ZN7testing8internal15TestFactoryImplI45DownloadManagerTest_TestDownloadFilename_TestE10CreateTestEv
 }
 {
-   bug_49750
-   Memcheck:Leak
-   fun:_Znw*
-   fun:_ZN16CookiesTreeModelC2EPN3net13CookieMonsterEP26BrowsingDataDatabaseHelperP30BrowsingDataLocalStorageHelperP26BrowsingDataAppCacheHelper
-   fun:_ZN26TabSpecificContentSettings27LocalSharedObjectsContainer19GetCookiesTreeModelEv
-   fun:-[CollectedCookiesWindowController loadTreeModelFromTabContents]
-   fun:-[CollectedCookiesWindowController initWithTabContents:]
-   fun:_ZN12_GLOBAL__N_154CollectedCookiesWindowControllerTest_Construction_Test8TestBodyEv
-}
-{
    bug_50281
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN*
    fun:_ZN30ChromeURLRequestContextFactoryC2EP7Profile
    fun:_ZN12_GLOBAL__N_122FactoryForOffTheRecordC2EP7Profile
    fun:_ZN29ChromeURLRequestContextGetter18CreateOffTheRecordEP7Profile
    fun:_ZN23OffTheRecordProfileImplC2EP7Profile
    fun:_ZN11ProfileImpl22GetOffTheRecordProfileEv
    fun:_ZN7Browser18NewIncognitoWindowEv
@@ skipping 80 matching lines @@
    bug_50638
    Memcheck:Cond
    fun:gleUpdateViewScissorData
    ...
    fun:cgl_set_surface
    fun:ogl_attach_surface
    fun:ogl_render_fade_transition
    fun:ogl_render_layer_
    fun:ogl_render_layers
 }