Suppress extensions leak on Mac.

tools/valgrind/memcheck/suppressions.txt

 # There are three kinds of suppressions in this file.
 # 1. third party stuff we have no control over
 #
 # 2. intentional unit test errors, or 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 (but a few aren't yet).
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 2682 matching lines @@
    fun:_ZN3net17DelayedSocketData12CompleteReadEv
    fun:_Z16DispatchToMethodIN3net17DelayedSocketDataEMS1_FvvEEvPT_T0_RK6Tuple0
    fun:_ZN27ScopedRunnableMethodFactoryIN3net17DelayedSocketDataEE14RunnableMethodIMS1_FvvE6Tuple0E3RunEv
    fun:_ZN11MessageLoop7RunTaskEP4Task
    fun:_ZN11MessageLoop21DeferOrRunPendingTaskERKNS_11PendingTaskE
    fun:_ZN11MessageLoop13DoDelayedWorkEPN4base4TimeE
    fun:_ZN4base19MessagePumpLibevent3RunEPNS_11MessagePump8DelegateE
    fun:_ZN11MessageLoop11RunInternalEv
    fun:_ZN11MessageLoop10RunHandlerEv
 }
+{
+   bug_42880
+   Memcheck:Leak
+   fun:_Znw*
+   fun:_ZN9__gnu_cxx13new_allocatorISt13_Rb_tree_nodeISt4pairIKSsSt3setIiSt4lessIiESaIiEEEEE8allocateEmPKv
+   fun:_ZNSt8_Rb_treeISsSt4pairIKSsSt3setIiSt4lessIiESaIiEEESt10_Select1stIS7_ES3_ISsESaIS7_EE11_M_get_nodeEv
+   fun:_ZNSt8_Rb_treeISsSt4pairIKSsSt3setIiSt4lessIiESaIiEEESt10_Select1stIS7_ES3_ISsESaIS7_EE14_M_create_nodeERKS7_
+   fun:_ZNSt8_Rb_treeISsSt4pairIKSsSt3setIiSt4lessIiESaIiEEESt10_Select1stIS7_ES3_ISsESaIS7_EE9_M_insertEPSt18_Rb_tree_node_baseSE_RKS7_
+   fun:_ZNSt8_Rb_treeISsSt4pairIKSsSt3setIiSt4lessIiESaIiEEESt10_Select1stIS7_ES3_ISsESaIS7_EE13insert_uniqueERKS7_
+   fun:_ZNSt8_Rb_treeISsSt4pairIKSsSt3setIiSt4lessIiESaIiEEESt10_Select1stIS7_ES3_ISsESaIS7_EE13insert_uniqueESt17_Rb_tree_iteratorIS7_ERKS7_
+   fun:_ZNSt3mapISsSt3setIiSt4lessIiESaIiEES1_ISsESaISt4pairIKSsS4_EEE6insertESt17_Rb_tree_iteratorIS8_ERKS8_
+   fun:_ZNSt3mapISsSt3setIiSt4lessIiESaIiEES1_ISsESaISt4pairIKSsS4_EEEixERS7_
+   fun:_ZN23ExtensionMessageService24DispatchEventToRenderersERKSsS1_bRK4GURL
+   fun:_ZL13DispatchEventP7ProfilePKcSs
+   fun:_ZN27ExtensionBrowserEventRouter12TabClosingAtEP11TabContentsi
+   fun:_ZN13TabStripModel16InternalCloseTabEP11TabContentsib
+   fun:_ZN13TabStripModel17InternalCloseTabsESt6vectorIiSaIiEEb
+   fun:_ZN13TabStripModel12CloseAllTabsEv
+   fun:_ZN7Browser12CloseAllTabsEv
+   fun:_ZN7Browser15OnWindowClosingEv
+   fun:-[BrowserWindowController windowShouldClose:]
+   fun:-[NSWindow _document:shouldClose:contextInfo:]
+   fun:-[NSWindow __close]
+   fun:-[NSWindow _close:]
+   fun:-[NSApplication sendAction:to:from:]
+}