GitLab

Make it easier to create der::Input's from constants by the magical
power of Templates.

Old and busted: der::Input foo(kFoo, arraysize(kFoo));
New hotness: der::Input foo(kFoo);

BUG=none
R=mattm@chromium.org

Review URL: https://codereview.chromium.org/1146283004

Cr-Commit-Position: refs/heads/master@{#330882}