The PDF loading documentation in extension_system.cc has be updated to
describe the new code paths.
To support delivery of input events to the mime handler renderer process it is
now necessary to route events via the correct RWHV interface. For Aura-based
platforms (Windows/Linux) this means RWHVAura::On*Event and for macOS this
means RWHVMac::RouteOrProcess*Event. Since Aura uses UI event types these have
become the source of truth on Aura-based platforms with conversion to Web event
types when needed (primarily for OSR).
This change also adds a timeout for CefProcessHostMsg_GetNewBrowserInfo to
avoid a hung renderer process if the guest WebContents route is not
registered via CefMimeHandlerViewGuestDelegate::OnGuestDetached as expected
prior to CefBrowserInfoManager::OnGetNewBrowserInfo being called. This
timeout can be disabled for testing purposes by passing the
`--disable-new-browser-info-timeout` command-line flag.
The `--disable-features=MimeHandlerViewInCrossProcessFrame` command-line
flag can be used for a limited time to restore the previous implementation
based on BrowserPlugin. That implementation will be deleted starting with
the 3897 branch update.
Known issues:
- ExecuteJavaScript calls on the frame hosting the PDF extension will not
be routed to the mime handler renderer process.
- The PDF extension will not load successfully if blocked by
ChromePluginPlaceholder and then manually continued via the "Run this
plugin" context menu option (see https://crbug.com/533069#c41).
