Various changes required to support ChromeVox Next to read Views and Windows.
- adds support for valueChanged event (e.g. to read adjustment of the volume slider)
- add textChanged event handler to process omnibox character echo/deletion.
- braille support for the textChanged,textSelectionChanged events
- whitelist ChromeVox for automation API up to stable.
- remove the --enable-chromevox-next cmd line flag.
- adds options for Output module (to only output braille, for example).
- adds a "dummy" alert window as a child of the desktop root node; this window will be used to fire alert events. Due to the way we support alerts now without backing views, this is necessary.
- start generating context for window on "enter". This picks up announcements like "status tray" when entering the status tray bar with alt+shift+s.
- exclude the first child (only child) of the desktop node from having a name set; this is because that particular window has a non-human readable name "Display<xxx>" which gets read frequently when entering a screen/display.
Review URL: https://codereview.chromium.org/
743273002
Cr-Commit-Position: refs/heads/master@{#306855}