win: Let about:version list the C++ compiler used to build chrome.

We're hoping to send out a single clang-built canary later this week, and
this will be useful for identifying that.  After that, we can remove this
row again.

BUG=82385,530785

Review URL: https://codereview.chromium.org/1404063002

Cr-Commit-Position: refs/heads/master@{#353930}
2 files changed