bug#15294: 24.3.50; js2-mode parser is several times slower in lexical-binding mode

[Stefan Monnier]

>> If it indeed comes from the handling of catch/throw, then there are two
>> ways to fix it:
>> - ...
>> - improve the byte-compiler so it can compile away cl-block/cl-return.
>> This should not require new byte-codes, but requires delving "deepish"
>> into the byte-compiler.
> This would take care of `cl-block' wrappers, but it would do nothing about
> explicit uses of `catch', right?

All js2-mode's uses of catch/throw can be replaced with
block/return, AFAICT (not that it's useful right now, since they'll
just be macroexpanded back to catch/throw).


        Stefan