views: Add support for accelerators (keyboard shortcuts)

[magreenblatt]

Original report by me.

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There are a few parts to this:

1. Support registration of accelerators with CefWindow and delivery via CefWindowDelegate.

A. Triggered accelerators will be delivered to the focused window first.

B. For CefBrowserView allow configuration of whether the CefBrowser gets an opportunity to handle the accelerator key event.

2. Support CefMenuButton focus and keyboard navigation.

A. Accelerators can be displayed in the menu using the existing CefMenuModel::SetAcceleratorAt method.

B. When a menu is focused it can be navigated using the keyboard (arrow keys, etc).

C. When a menu is focused character shortcuts can be displayed and enabled using the & character in the menu item label (e.g. "E&xit" will underline 'x' in the label, and pressing the letter X will trigger the command).

3. Add a callback for unhandled key events at the CefWindow level. This can be used, for example, to focus the MenuButton when the ALT key is pressed (and unhandled by any other control).

[magreenblatt]

Attached focused_menu.png is an example of what the focused CefMenuButton with accelerator and mnemonic (underlined) characters looks like.

[magreenblatt]

Some notes on relevant code paths in Chromium:

• Accelerators are registered with FocusManager::RegisterAccelerator and notifications are delivered via FocusManager::OnKeyEvent.
• Unhandled accelerators could be exposed via FocusManagerDelegate::ProcessAccelerator. In that case the FocusManager would need to be created using a custom FocusManagerFactory installed via FocusManagerFactory::Install. New CEF API would need to be added in that case for exposing global views-related notifications.
• For WebView pre-processing of accelerators is controlled by WebView::set_allow_accelerators and WebView::SkipDefaultKeyEventProcessing. When accelerators are not pre-processed they must be forwarded to FocusManager via WebContentsDelegate::HandleKeyboardEvent and views::UnhandledKeyboardEventHandler.
• Menu button focus on click is handled in MenuButton::OnMousePressed. Keyboard navigation is handled in MenuButton::OnKeyPressed.
• Rendering of menu item mnemonic (underline) is handled via MenuItemView::GetDrawStringFlags and gfx::Canvas::HIDE_PREFIX. Rendering of menu item accelerator text (e.g. "Alt+X") is handled via MenuItemView::PaintMinorText.

[magreenblatt]

It should be sufficient to handle key events at the window level for focus-related changes. We might in the future expose an unhandled key event callback at the control (CefView) level if necessary.

[magreenblatt]

Done in master revision bd1b801 (bb) and 2987 branch revision e31a44a (bb).

[magreenblatt]

Master revision 6ed4fe9 (bb) and 2987 branch revision 368273c (bb) adds groups (associated controls that support focus traversal with arrow keys) and focus/blur callbacks.

• cefclient: Only make menus focusable when ALT is pressed.
• cefclient: Display sample top menu when passed the --show-top-menu command-line flag.

[magreenblatt]

Master revision 6eaf11f (bb) and 2987 branch revision 874e670 (bb) add support for top menu switching using mouse and arrow keys.

• cefclient: Add example ViewsMenuBar implementation and show top menu by default (specify --hide-top-menu to hide it).

[magreenblatt]

Master revision 16125bd (bb) and 2987 branch revision b0c8a34 (bb) add support for mnemonic (underlined) characters in MenuButton labels.

[magreenblatt]

Support ink drop effect on buttons in master revision 10f9a94 (bb) and 2987 branch revision d6eff7d (bb). Fix layout calculation for LabelButton with mnemonics in master revision b08f0ed (bb) and 2987 branch revision 68b0352 (bb). Support styling of menus in master revision 8fa8af3 (bb) and 2987 branch revision c2a87c8 (bb).

• cefclient: Pass --use-views --background-color=black command-line flags to see the result of menu styling.

[magreenblatt]

• set attachment to "focused_menu.png"

[magreenblatt]

• edited description

[magreenblatt]

• changed state from "new" to "resolved"