Add a simpler CanZoom/Zoom API as an alternative to the more error-prone
SetZoomLevel/GetZoomLevel API. Both APIs are now implemented for both runtimes.
With the Chrome runtime a zoom notification bubble will be displayed unless
CefBrowserSettings.chrome_zoom_bubble is set to STATE_DISABLED.
To test:
- Run cefclient and select zoom entries from the Tests menu.
- chrome: Run cefclient with `--hide-chrome-bubbles` command-line flag to hide
the zoom notification bubble.