initial version of a chrome extension library

more files added to the commit
Merge pull request #49 from dart-gde/ext_api

initial version of a chrome extension library
Add ChromeCompleter class to common.dart.
Add windows.dart to provide support for the chrome.windows APIs.
Added more tests.

Add missing windowId parameter to update method.
moving to common class layout
Merge pull request #1 from financeCoding/DrMarcll_master

Add top level final instance of Windows
Address pull request comments.
Remove extraneous js.retain.
Merge pull request #50 from DrMarcII/master

Add support for chrome.windows APIs
added a library to reference all extension tests
Merge pull request #51 from dart-gde/windows_tweak

added a library to reference all extension tests