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}
bool GuestViewBase::IsPreferredSizeModeEnabled() const {
  return false;
}

bool GuestViewBase::IsPreferredSizeModeEnabled() const {
  return false;
}
