Make win_clang trybot non-experimental.
Make win_clang trybot non-experimental.

It seems to be working well, let's try using it for real.

BUG=588518

Review URL: https://codereview.chromium.org/1849103002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#387048}

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