Add kDevicePolicyExternalDataResourceCacheSize in policy_constants.

This allows not to configure size of ResourceCache for external data type device policies manually,
but to use generated value.

Bug: 814364
Change-Id: If8b255595de754ca3428498aa6926a3e7265b462
Reviewed-on: https://chromium-review.googlesource.com/c/1448317
Commit-Queue: Nikita Podguzov <nikitapodguzov@google.com>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Lutz Justen <ljusten@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628713}
3 files changed