libc++/win/natvis: Add visualizer for std::map.

Thanks to Eric Feiveson <[email protected]> for suggesting to rely
on the typedefs in std::map<> which was critical for getting this working.

Bug: 947911
Change-Id: I2a73061698d45ace2eaf859534f696a86542d35b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574820
Auto-Submit: Nico Weber <[email protected]>
Commit-Queue: Thomas Anderson <[email protected]>
Reviewed-by: Thomas Anderson <[email protected]>
Cr-Commit-Position: refs/heads/master@{#652382}
1 file changed