Fix leak in generated credit card bubble tests.

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 # running overnight and removing outdated bugs/suppressions.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 831 matching lines @@
    fun:chromeos::NetworkCertMigratorTest::CleanupTestCert
 }
 {
    bug_270312
    Heapcheck:Leak
    ...
    fun:MessageCenterButtonBar
    fun:MessageCenterView
    fun:message_center::MessageCenterViewTest::SetUp
 }
-{
-   bug_271431
-   Heapcheck:Leak
-   ...
-   fun:CreateBubble
-   fun:autofill::GeneratedCreditCardBubbleController::Show
-   fun:autofill::GeneratedCreditCardBubbleController::SetupAndShow
-   fun:autofill::GeneratedCreditCardBubbleController::Show
-}