Relative links in markdown result in broken links

[GoogleCodeExporter]

What steps will reproduce the problem?
1. In a/b/c/README.md, add a link: [test](../../foo/bar).
2. Observe rendered URL

Expected: links to a/foo/bar in the repository
Actual: links to afoo/bar

e.g.  in 
https://chromium.googlesource.com/chromium/src/+/9248cc7/third_party/WebKit/Sour
ce/platform/graphics/paint/README.md:

../../transforms/TransformationMatrix.h is resolved to 
https://chromium.googlesource.com/chromium/src/+show/9248cc7/third_party/WebKit/
Source/platformtransforms/TransformationMatrix.h

Probably just a trivial case of a missing "/" being added to the URL in 
MarkdownToHtml.

Original issue reported on code.google.com by jbroman@chromium.org on 13 Oct 2015 at 6:03