Make ui gn check pass. Misc GN build improvements.

Content/public/app was messed up and didn't link everything properly, so this separates it out into browser and child like content/app is.

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/545313002

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Cr-Mirrored-Commit: b41a8d6e789ac5df9a6d314cd0ad59f584f53dea