A CefBrowserHostImpl is created using a CefRequestContextImpl that may have a
CefRequestContextHandler. Multiple CefRequestContextImpl may share the same
underlying CefBrowserContext which owns a CefResourceContext. IO-thread
callbacks from Chromium are often associated with a CefResourceContext and the
target frame is identified using render_process_id/render_frame_id routing IDs.
This change forwards frame create/delete notifications from CefBrowserHostImpl
(or CefMimeHandlerViewGuestDelegate) to CefResourceContext so that it can
properly resolve the association from routing ID to Handler when queried from
CefPluginServiceFilter::IsPluginAvailable.
To test: Verify that all ceftests pass with NetworkService disabled.
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