This makes it possible for the consumers of the content settings API to
store different types of information.

Additional mechanical change:
Move some of the methods from
content_settings/core/browser/content_settings_utils.h to
content_settings/core/common/content_settings_utils.h.
This makes it possible to access the moved methods from chrome/renderer.

BUG=735518
TBR=sdefresne@chromium.org

Review-Url: https://codereview.chromium.org/2938163002
Cr-Commit-Position: refs/heads/master@{#483829}