Deduplicated or renamed supervised_user variables

This is a preparatory patch for jumbo compilations where several
cc files are compiled in the same translation unit. Then you get
compilation errors if they all define their own kNumRetries and
kBackoffPolicy, kApiPath and so on.

This patch gives the 5 different kNumRetries variables and 3
different kBackoffPolicy variables in chrome/browser
their own name. It also renames kApiPath, kApiUrl and kApiScope.

It also deduplicates a kAuthorizationHeaderFormat string that had
4 different instances.

Bug: 746957
Change-Id: Ib14ccaa372d3b28cd505b2e7cec519a5635e3173
Reviewed-on: https://chromium-review.googlesource.com/868335
Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Reviewed-by: Cathy Li <chili@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#534084}
12 files changed