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This adds a Connect method to SerialService and a new partly complete
Connection interface. This change includes methods for:
- setting connection options
- getting connection info
- setting host control signals
- getting device control signals
- flushing buffers

BUG=389016

Review URL: https://codereview.chromium.org/401563002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284399 0039d316-1c4b-4281-b951-d872f2087c98