Bug 887334 - Enter a compartment between manual calls to JS_{Save,Restore}FrameChain. r=luke

The stuff in nsXBLProtoImplMethod is doing the same thing, so let's just have
it call into nsJSUtils.

content/xbl/src/nsXBLProtoImplMethod.cpp

@@ -347,10 +347,7 @@ nsXBLProtoImplAnonymousMethod::Execute(nsIContent* aBoundElement)
     // anything else.  We just report it.  Note that we need to set aside the
     // frame chain here, since the constructor invocation is not related to
     // whatever is on the stack right now, really.
-    JSBool saved = JS_SaveFrameChain(cx);
-    JS_ReportPendingException(cx);
-    if (saved)
-        JS_RestoreFrameChain(cx);
+    nsJSUtils::ReportPendingException(cx);
     return NS_ERROR_FAILURE;
   }
 

dom/base/nsJSUtils.cpp

@@ -143,7 +143,10 @@ nsJSUtils::ReportPendingException(JSContext *aContext)
 {
   if (JS_IsExceptionPending(aContext)) {
     bool saved = JS_SaveFrameChain(aContext);
-    JS_ReportPendingException(aContext);
+    {
+      JSAutoCompartment ac(aContext, js::GetDefaultGlobalForContext(aContext));
+      JS_ReportPendingException(aContext);
+    }
     if (saved) {
       JS_RestoreFrameChain(aContext);
     }