chrome: Add support for off-screen rendering

[magreenblatt]

Original report by me.

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This issue involves the following functionality currently supported by the Alloy runtime:

• Off-screen rendering (OSR) via CefWindowInfo.SetAsWindowless and CefRenderHandler

Most likely to be supported for the Chrome runtime via the Ozone layer (see issue #3263).

The following capabilities would need to be implemented in combination with OSR support:

• File and JS dialog handlers (CefDialogHandler, CefJSDialogHandler; needed for DialogTest.*, JSDialogTest.*, LifeSpanTest.*; currently uses default Chrome dialogs).
• Context menu custom runner (CefContextMenuHandler::RunContextMenu; currently uses default Chrome menu)

See issue #2969 for background on the Chrome runtime.

[magreenblatt]

Use Chrome file dialogs on all platforms and runtimes (fixes issue #3314)

All file dialogs irrespective of source, platform and runtime will now be routed through CefFileDialogManager and trigger CefDialogHandler callbacks (see issue #3293).

Adds Chrome runtime support for CefBrowserHost::RunFileDialog and CefDialogHandler callbacks.

Adds Alloy runtime support for internal GTK file and print dialogs on Linux subject to the following limitations:

1. Internal GTK implementation:
   • Cannot be used with multi-threaded-message-loop because Chromium's internal GTK implementation is not thread-safe (does not use GDK threads).
   • Dialogs will not be modal to application windows when used with off-screen rendering due to lack of access to the client's top-level GtkWindow.
2. Cefclient CefDialogHandler implementation:
   • Cannot be used with Views because it requires a top-level GtkWindow.

Due to the above limitations no dialog implementation is currently provided for Views + multi-threaded-message-loop on Linux. In cases where both implementations are supported the cefclient version is now behind an optional --use-client-dialogs command-line flag.

Expressly forbids multiple simultaneous file dialogs with the internal platform implementation which uses modal dialogs. CefDialogHandler will still be notified and can optionally handle each request without a modal dialog (see issue #3154).

Removes some RunFileDialog parameters that are not supported by the Chrome file dialog implementation (selected_accept_filter parameter, cef_file_dialog_mode_t overwrite/read-only flags).

→ <<cset 2ea7459a89fb (bb)>>

[magreenblatt]

• edited description

[magreenblatt]

• edited description

[magreenblatt]

This will be completed in issue #3681 (OSR = Chrome bootstrap + Alloy style).