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Before they were part of the interface, which should be clean and simple.
Moreover, this CL lets pass the list of changes via ProvidedFileSystemObserver
which will be required soon in the Service class.

TEST=unit_tests, browser_tests: *FileSystemProvider*
BUG=248427

Review URL: https://codereview.chromium.org/663713002

Cr-Commit-Position: refs/heads/master@{#300071}