Moved guest_view_registry to GuestViewManager and made it an instance map

This change allows for the change towards moving GuestViewManager to components
and implementing an extensions specific GuestViewManager that installs extensions-specific
guest types.

BUG=444869

Review URL: https://codereview.chromium.org/1096623002

Cr-Commit-Position: refs/heads/master@{#325919}
void GuestViewBase::RunFileChooser(WebContents* web_contents,
                                   const content::FileChooserParams& params) {
  if (!attached() || !embedder_web_contents()->GetDelegate())
    return;

  embedder_web_contents()->GetDelegate()->RunFileChooser(web_contents, params);
}

void GuestViewBase::RunFileChooser(WebContents* web_contents,
                                   const content::FileChooserParams& params) {
  if (!attached() || !embedder_web_contents()->GetDelegate())
    return;

  embedder_web_contents()->GetDelegate()->RunFileChooser(web_contents, params);
}
