Fix my memory leak in MessageChannel

tools/heapcheck/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 # running overnight and removing outdated bugs/suppressions.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 1224 matching lines @@
    Heapcheck:Leak
    ...
    fun:UserStyleSheetWatcherTest_StyleLoad_Test::TestBody
 }
 {
    bug_76644_b
    Heapcheck:Leak
    ...
    fun:UserStyleSheetWatcher::Init
 }
-{
-   bug_77258_a
-   Heapcheck:Leak
-   fun:webkit::ppapi::::MessageChannelAllocate
-   fun:_NPN_CreateObject
-   fun:WebKit::WebBindings::createObject
-   fun:MessageChannel
-   fun:PluginInstance
-   fun:webkit::ppapi::PpapiUnittest::SetUp
-}
-{
-   bug_77258_b
-   Heapcheck:Leak
-   fun:webkit::ppapi::::MessageChannelAllocate
-   fun:_NPN_CreateObject
-   fun:WebKit::WebBindings::createObject
-   fun:MessageChannel
-   fun:PluginInstance
-   fun:webkit::ppapi::ResourceTrackerTest_*_Test::TestBody
-}