We don't want to check for exceptions after every single line on our runtime methods. A better way to handle this is to add the check in all methods that have direct side effects (as e.g. writing to a property of the JS stack). We also need to return whereever we throw an exception. To simplify the code, ExecutionContext::throwXxx methods now return a ReturnedValue (always undefined) for convenience. Change-Id: Ide6c804f819c731a3f14c6c43121d08029c9fb90 Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>