Fix memory leak in ExtensionWebRequestTest, and remove the suppressions for it.

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 # running overnight and removing outdated bugs/suppressions.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 1604 matching lines @@
    Heapcheck:Leak
    ...
    fun:TestingProfile::GetWebKitContext
 }
 {
    bug_85151_b
    Heapcheck:Leak
    ...
    fun:WebKitContextTest_Basic_Test::TestBody
 }
-{
-   bug_85641
-   Heapcheck:Leak
-   ...
-   fun:ExtensionEventRouter::DispatchEvent
-   fun:ExtensionWebRequestEventRouter::DispatchEvent
-}