new method SetRootedScriptObject. bug 43466 r=brendan

dom/public/nsIScriptContext.h

@@ -330,6 +330,16 @@ public:
   NS_IMETHOD SetTerminationFunction(nsScriptTerminationFunc aFunc,
                                     nsISupports* aRef) = 0;
 
+  /**
+   * Store a single script object to be unrooted from the script garbage
+   * collector in the implementation's destructor. This obvious hack
+   * is used to delay the unrooting of an object until that point.
+   * (At time of writing, it's used only on the window script object).
+   * This should never be called twice (the stored object will never
+   * be replaced.)
+   */
+  NS_IMETHOD SetRootedScriptObject(void *aObject) = 0;
+
   /**
    * Called to disable/enable script execution in this context.
    */

dom/src/base/nsJSEnvironment.h

@@ -49,6 +49,7 @@ private:
   nsCOMPtr<nsISupports> mRef;
   PRBool mScriptsEnabled;
   PRUint32 mBranchCallbackCount;
+  void *mRootedScriptObject; // special case for the window script object
 
   static JSBool PR_CALLBACK DOMBranchCallback(JSContext *cx, JSScript *script);
   
@@ -127,6 +128,7 @@ public:
   NS_IMETHOD GetOwner(nsIScriptContextOwner** owner);
   NS_IMETHOD SetTerminationFunction(nsScriptTerminationFunc aFunc,
                                     nsISupports* aRef);
+  NS_IMETHOD SetRootedScriptObject(void *aObject);
   NS_IMETHOD GetScriptsEnabled(PRBool *aEnabled);
   NS_IMETHOD SetScriptsEnabled(PRBool aEnabled);