Bug 1521191, part 3 - Add a function to create a negative leak. r=froydnj

This is needed to test the test harness's handling of a negative leak
being reported by the XPCOM leak checker.

Depends on D17535

Differential Revision: https://phabricator.services.mozilla.com/D17536

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

js/xpconnect/idl/xpccomponents.idl

@@ -329,6 +329,12 @@ interface nsIXPCComponents_Utils : nsISupports
      */
     void intentionallyLeak();
 
+    /*
+     * In a debug build, cause the XPCOM leak checker to report a negative leak.
+     * This is needed to test leak checking.
+     */
+    void intentionallyLeakNegatively();
+
     /*
      * In a debug build, make XPCOM not print out a bloat log in this process.
      * This is needed to test leak checking.

js/xpconnect/src/XPCComponents.cpp

@@ -1758,6 +1758,16 @@ nsXPCComponents_Utils::IntentionallyLeak() {
 #endif
 }
 
+NS_IMETHODIMP
+nsXPCComponents_Utils::IntentionallyLeakNegatively() {
+#ifdef DEBUG
+  MOZ_COUNT_DTOR(IntentionallyLeakedObject);
+  return NS_OK;
+#else
+  return NS_ERROR_NOT_IMPLEMENTED;
+#endif
+}
+
 NS_IMETHODIMP
 nsXPCComponents_Utils::DisableDumpStatistics() {
 #ifdef DEBUG