Suppress an invalid read in extension notifications

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 # running overnight and removing outdated bugs/suppressions.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 3535 matching lines @@
    bug_47331_part_2
    Memcheck:Leak
    fun:malloc
    fun:malloc
    fun:sqlite3MemMalloc
    fun:mallocWithAlarm
    fun:sqlite3Malloc
    fun:sqlite3HashInsert
    fun:sqlite3EndTable
 }
+{
+   bug_47863
+   Memcheck:Addr4
+   ...
+   fun:_ZN21ExtensionsServiceTest7ObserveE16NotificationTypeRK18NotificationSourceRK19NotificationDetails
+   fun:_ZN19NotificationService6NotifyE16NotificationTypeRK18NotificationSourceRK19NotificationDetails
+   fun:_ZN17ExtensionsService21NotifyExtensionLoadedEP9Extension
+   fun:_ZN17ExtensionsService17OnExtensionLoadedEP9Extensionb
+   fun:_ZN17ExtensionsService22LoadInstalledExtensionERK13ExtensionInfob
+   fun:_ZN17ExtensionsService25ContinueLoadAllExtensionsEPSt6vectorI10linked_ptrI13ExtensionInfoESaIS3_EEN4base9TimeTicksEb
+   fun:_ZN17ExtensionsService17LoadAllExtensionsEv
+   fun:_ZN17ExtensionsService16ReloadExtensionsEv
+}