This change adds a new mochitest-only helper called `AppTestDelegate`. This
helper will provide primitives that are not normally available at the toolkit
level.
Each app can implement the `AppUiTestDelegate` API to provide the primitives.
This is done so that we can ensure compatibility of the Extension API across
implementations.
The initial set of APIs is as follows:
```
class TestDelegate {
clickPageAction(window, extensionId);
closePageAction(window, extensionId);
clickBrowserAction(window, extensionId);
closeBrowserAction(window, extensionId);
awaitExtensionPanel(window, extensionId);
// Returns a unique identifier for the tab
openNewForegroundTab(window, url, waitForLoad);
// tabId must be the identifier from openNewForegroundTab
removeTab(tabId);
}
```
Differential Revision: https://phabricator.services.mozilla.com/D99170
dd9a63f7e4