Delay creation of many decl caches in our decls.
Avoid looking up an enclosing decl when doing privacy checks if hte member isn't actually private.
Avoid getting the enclosing decl early if we only need it to report an error.
Remove code constructs that cause V8 to not optimize methods.

Using 'arguments' prevents optimization.
Using 'try/finally' prevents optimization.
remove constructs that affect some javascript optimizers.
Use 'Object.create(null)' as the idiomatic way to get a string dictionary.
Store less data in a comment node.
Some small optimizations to help the javascript JITs.
Release rewind point as soon as possible.
Update LKG.
Update with code review comments