importer: Refactor ImporterList so it doesn't have to know about Importer.

- Move CreateImporterByType to importer_type.h
- Rename ProfileType to ImporterType to clarify its usage.
- Rename the variable names used for ProfileType from browser_type to
importer_type as we support importing from more than just browsers.
- Cleanup a few comments.
- Remove unneed importer_list.h includes.
- This also makes the ImporterHost not to know about ImporterList.

BUG=None
TEST=None

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Review URL: http://codereview.chromium.org/6693056

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@80362 0039d316-1c4b-4281-b951-d872f2087c98
19 files changed