Reapply "Rename mappedBy to map."
Reapply "Rename mappedBy to map."

This reverts commit r17907.

TBR.

Review URL: https://codereview.chromium.org//12090093

git-svn-id: d21bfdc9f98bb697a501ab295d9b4211dc860b14@17918 260f80e4-7a28-3924-810f-c04153c831b5

dart-lang/path