Create c/b/ui/views/layout_constants.*.
This becomes a global place to get views layout constants which need some kind
of parametrized getter, in these cases because of Material Design. Previously
these were accessible from ThemeService, but that required having an instance of
a ThemeProvider (infeasible in some contexts) and implied these were
theme-related in some way, which isn't true.
BUG=531544
TEST=none
Review URL: https://codereview.chromium.org/
1338103002
Cr-Commit-Position: refs/heads/master@{#348967}