IDL: Improve "argument needs v8::TryCatch" logic slightly

Source/bindings/tests/results/V8TestObject.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file has been auto-generated by code_generator_v8.py. DO NOT MODIFY!
 
 #include "config.h"
 #include "V8TestObject.h"
 
 #include "bindings/core/v8/BindingSecurity.h"
@@ skipping 6634 matching lines @@
 
 static void voidMethodTestEnumArgMethod(const v8::FunctionCallbackInfo<v8::Value>& info)
 {
     if (UNLIKELY(info.Length() < 1)) {
         V8ThrowException::throwException(createMinimumArityTypeErrorForMethod("voidMethodTestEnumArg", "TestObject", 1, info.Length(), info.GetIsolate()), info.GetIsolate());
         return;
     }
     TestObject* impl = V8TestObject::toNative(info.Holder());
     V8StringResource<> testEnumTypeArg;
     {
-        v8::TryCatch block;
-        V8RethrowTryCatchScope rethrow(block);
         TOSTRING_VOID_INTERNAL(testEnumTypeArg, info[0]);
         String string = testEnumTypeArg;
         if (!(string == "" || string == "EnumValue1" || string == "EnumValue2" || string == "EnumValue3")) {
             V8ThrowException::throwTypeError(ExceptionMessages::failedToExecute("voidMethodTestEnumArg", "TestObject", "parameter 1 ('" + string + "') is not a valid enum value."), info.GetIsolate());
             return;
         }
     }
     impl->voidMethodTestEnumArg(testEnumTypeArg);
 }
 
@@ skipping 4617 matching lines @@
             // FIXME: We should support more exceptions.
             RELEASE_ASSERT_NOT_REACHED();
         }
         block.ReThrow();
         return false;
     }
     return true;
 }
 
 } // namespace blink