Add chrome.permissions API

This also converts the USB example to use it for the additional permission request.
Some cleanups of the tree.
Change a = to a : to placate dart_analyzer
Update usb.dart

ls.scoped() ==> js.scoped()
Add usb example to hop's analyzer example test
Fix uo some mis-named hop tasks.
update versions
Merge pull request #29 from AmandaCameron/permissions-api

Implements the permissions API
clean up analyzer warnings
Merge pull request #31 from dart-gde/cleanup

clean up analyzer warnings
Merge pull request #30 from dart-gde/versions

update versions
Merge pull request #32 from AmandaCameron/cleanup-compiles

Cleanups as specified in Issue #27