importer: Cleanup the names of files and classes under ui/views/importer directory.

- Match the names of the files with the current pattern used in the ui/gtk/importer directory.
- Add OVERRIDE to a bunch of virtual methods.

BUG=None
TEST=existing unit_tests.

Review URL: http://codereview.chromium.org/6613017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@76859 0039d316-1c4b-4281-b951-d872f2087c98
15 files changed