Accessibility support

[cztomczak]

See CefAccessibilityHandler:
https://github.com/chromiumembedded/cef/search?q=CefAccessibilityHandler

Related:

• command line flag: --force-renderer-accessibility
• Example implementation in upstream cefclient, see tests/cefclient/browser/osr_accessibility_* files:

  • https://github.com/chromiumembedded/cef/blob/master/tests/cefclient/browser/osr_accessibility_node_win.cc

  • https://github.com/chromiumembedded/cef/blob/master/tests/cefclient/browser/osr_accessibility_node_mac.mm

  • https://github.com/chromiumembedded/cef/blob/master/tests/cefclient/browser/osr_accessibility_helper.cc

  • https://github.com/chromiumembedded/cef/blob/master/tests/cefclient/browser/osr_accessibility_node.cc

Doc comments from cef_browser.h:

///
  // Set accessibility state for all frames. |accessibility_state| may be
  // default, enabled or disabled. If |accessibility_state| is STATE_DEFAULT
  // then accessibility will be disabled by default and the state may be further
  // controlled with the "force-renderer-accessibility" and
  // "disable-renderer-accessibility" command-line switches. If
  // |accessibility_state| is STATE_ENABLED then accessibility will be enabled.
  // If |accessibility_state| is STATE_DISABLED then accessibility will be
  // completely disabled.
  //
  // For windowed browsers accessibility will be enabled in Complete mode (which
  // corresponds to kAccessibilityModeComplete in Chromium). In this mode all
  // platform accessibility objects will be created and managed by Chromium's
  // internal implementation. The client needs only to detect the screen reader
  // and call this method appropriately. For example, on macOS the client can
  // handle the @"AXEnhancedUserInterface" accessibility attribute to detect
  // VoiceOver state changes and on Windows the client can handle WM_GETOBJECT
  // with OBJID_CLIENT to detect accessibility readers.
  //
  // For windowless browsers accessibility will be enabled in TreeOnly mode
  // (which corresponds to kAccessibilityModeWebContentsOnly in Chromium). In
  // this mode renderer accessibility is enabled, the full tree is computed, and
  // events are passed to CefAccessibiltyHandler, but platform accessibility
  // objects are not created. The client may implement platform accessibility
  // objects using CefAccessibiltyHandler callbacks if desired.
  ///
  /*--cef()--*/
  virtual void SetAccessibilityState(cef_state_t accessibility_state) = 0;

For implementation hints see calls to SetAccessibilityState in upstream CEF source codes:
https://github.com/chromiumembedded/cef/search?q=SetAccessibilityState&unscoped_q=SetAccessibilityState

See chrome://accessibility url.

[cztomczak]

Done in rev e72609c. New APIs: Browser.SetAccessibilityState, AccessibilityHandler for OSR mode.