Handling cancel buttons
Including menu transition in test
- Removed clickCancelButton and replaced with clickButtonWithTitle().
- Added specific dialogs and rearrangeed how they're setup and linked with menus (the menu item doesn't instantiate anymore, and, instead, just takes a reference).
- Created specific AboutDialogAccess with custom methods for capabilities only aboutDialog has (clickDoneButton).  This is how future dialog controls will be setup.
Merge commit '807a1cbf1f44309a18e202d875d65d08adbd3ca3' into umop-testing-ui-cancel_buttons
Resolved conflicts & Added override dialog support to openAndCloseWithButton
Resolved conflicts
Merge commit 'a980e338e016d21b7d953b35f589587ddff87e57' into umop-testing-ui-cancel_buttons
Merge branch 'umop-testing-ui-dialogs' into umop-testing-ui-cancel_buttons
Cleaned up
Tightened up abstraction of dialogs
Added comment
Switched to traditional singleton `.instance` static getter rather than factory.
Review fixes & nits
Merge branch 'master' of https://github.com/dart-lang/chromedeveditor into umop-testing-ui-cancel_buttons
Merge pull request #2932 from dart-lang/umop-testing-ui-cancel_buttons

Refactoring testing code and testing ui cancel buttons