[PATCH] Add an optional mapping from source paths to source contents.

[Dmitri Gribenko]

  I am not an expert in compilation database architecture.  But here's my comment: usually multiple source files in a single database depend on the same set of headers.  It seems like the proposed API forces us to duplicate header contents in memory for every file that uses the header.

http://llvm-reviews.chandlerc.com/D2121