GitLab

2 notable changes
1) Moved this inside an NS_ENUM inside the web namespace for
consistency with BrowsingDataTypes

2) Changed SYNCHRONIZING to CHANGING for 2 reasons
- It better reflects the actual intent of this enum value.
SYNCHRONIZING does not mean much in the context of the
CRWBrowsingDataStore since it's unclear
which object it's trying to synchronize with.
- To avoid confusion with |BrowsingDataParition::IsSynchronized|

BUG=480654

Review URL: https://codereview.chromium.org/1146223012

Cr-Commit-Position: refs/heads/master@{#333135}