Allow compiling in WHITESPACE mode

[ribrdb]

We're using WHITESPACE instead of BUNDLE because bundle doesn't support source maps.
(That doesn't fix source maps for j2cl code, but at least source maps for non-j2cl code still works)

[gkdn]

J2CL already suppresses this as file level:

j2cl/transpiler/java/com/google/j2cl/generator/JavaScriptImplGenerator.java

Line 117 in d764bd7

"unusedLocalVariables",

Could you clarify why you need this here? Maybe it is your own file?

[niloc132]

As a possible alternative, we made a small patch to BUNDLE mode which adds sourcemaps (example running at https://colinalworth.com/boxes-and-lines-j2cl-devmode/), since we found running closure in BUNDLE mode to be rather faster than WHITESPACE (no need to fully parse the AST, just look for dependencies). We have not kept this up to date, since upstream closure removed the PersistentInputStore feature, which we also used to allow for keeping unchanged files and their dependencies cached in closure, but could look at trying to rebase it if there was interest.

Vertispan/closure-compiler@0c394bf

[ribrdb]

I don't have the logs handy at the moment, but was definitely getting this error for j2cl's internal packages without this change. I'm not sure why the suppression inside the file wouldn't work.
@niloc132 if we can get sourcemaps working in bundle mode that sounds much better. Whitespace compilation is still pretty slow.

[MrbrooksIsSilent]

Data Monitoring

[gkdn]

Reproduced the issue and filed #40