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This will be used by the VariationsService to simulate newly
received variations seed, to evaluate whether there's sufficient
new changes to badge the UI to suggest a restart (similar to
what happens during auto updates).

This is the initial version of this class and still
has some missing pieces, left as TODOs.

BUG=315807
TEST=Unit tests.
TBR=joi@chromium.org

Review URL: https://codereview.chromium.org/41623002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243600 0039d316-1c4b-4281-b951-d872f2087c98