bug 1524478 - don't create JS objects from WebAuthnManager or U2F destructors r=qdot

Before this patch, the WebAuthnManager/U2F destructors would call MaybeReject on
existing transaction promises. Doing this leaks JS objects. If
WebAuthnManager/U2F are being destructed, though, the window is going away, so
it shouldn't be necessary to reject any outstanding promises. This patch just
clears the transactions.

Differential Revision: https://phabricator.services.mozilla.com/D27346

--HG--
extra : moz-landing-system : lando

dom/u2f/U2F.cpp

@@ -140,7 +140,7 @@ U2F::~U2F() {
   MOZ_ASSERT(NS_IsMainThread());
 
   if (mTransaction.isSome()) {
-    RejectTransaction(NS_ERROR_ABORT);
+    ClearTransaction();
   }
 
   if (mChild) {

dom/webauthn/WebAuthnManager.cpp

@@ -200,7 +200,7 @@ WebAuthnManager::~WebAuthnManager() {
   MOZ_ASSERT(NS_IsMainThread());
 
   if (mTransaction.isSome()) {
-    RejectTransaction(NS_ERROR_ABORT);
+    ClearTransaction();
   }
 
   if (mChild) {