Allow mapping of Java source files.

[advayDev1]

No description provided.

[confile]

@advayDev1 whar is this good for compared with translateSourcepaths.

[advayDev1]

I'm currently using it for the following:
I have a third-party library which almost meets my needs (and comes with a source jar).
I need to however alter some native implementations substantially. I map just those 3 files to brand new Java files.

translateSourcepaths works only if I was using this library in exactly one other project AND i was willing to use --build-closure. Instead I chose to build this third-party library using the new j2objcTranslation feature I added in #431. I've gotten rid of all --build-closure in all of my projects using the new dependency features and it speeds up my build by a factor about 5 when I change a single file (in the past build-closure meant everything had to be rebuilt)

[brunobowden]

Change ret => result, I think it's more legible.

[brunobowden]

Actually, it seems like ret is a convention so shall we stick with that?

[advayDev1]

yep it is

[brunobowden]

LGTM

Yet another example of why cycleFinder and translate should have a shared base class ;-)