Changes

* Brendan and Jim Blandy have suggested that using a separate mapping file will work better than including the mapping in the generated source.

* A [https://bugs.webkit.org/show_bug.cgi?id=60550 bug with a patch] was opened for WebKit but closed INVALID.** Webkit has [https://bugs.webkit.org/show_bug.cgi?id=30933 another bug] open for this feature.