Drop unnecessary v8::TryCatch in V8StringResource::prepare()

LayoutTests/fast/events/before-unload-return-bad-value.html

Index: LayoutTests/fast/events/before-unload-return-bad-value.html
diff --git a/LayoutTests/fast/events/before-unload-return-bad-value.html b/LayoutTests/fast/events/before-unload-return-bad-value.html
index 4a7d6d5c25aaba530155c60d2cee897f10a2e73c..5fad9b9da43cea540c9c45ab793d58f3886978a6 100644
--- a/LayoutTests/fast/events/before-unload-return-bad-value.html
+++ b/LayoutTests/fast/events/before-unload-return-bad-value.html
@@ -6,7 +6,12 @@
 description("Tests that an exception is thrown when the value returned in the beforeunload callback cannot be converted to a String");
 window.jsTestIsAsync = true;
 
+var alreadyTested = false;
 function test(frame) {
+    if (alreadyTested)
+        return;
+    alreadyTested = true;
+
     frame.contentWindow.onbeforeunload = function(event) {
         return {toString: function() { throw "Exception in toString()"; }};
     };
@@ -20,7 +25,6 @@ window.onerror = function(msg) {
     testMessage = msg;
     testPassed("Exception was thrown");
     shouldBeEqualToString("testMessage", "Uncaught Exception in toString()");
-    setTimeout(finishJSTest, 0);
     return true;
 };
 </script>