Allow methods and signals on the org.freedesktop.DBus.Properties interface.

Allow methods and signals on the org.freedesktop.DBus.Properties interface.

This is needed to allow cromo plugins to send the MmPropertiesChanged modem manager signal.

BUG=chromium-os:4667
TEST=Build cromo. Compare generated files before and after this change.
Observe that the code generated for mm-modem.xml now defines
MmPropertiesChanged, where before it did not. Checked that nothing
else has changed in the generated code.

Change-Id: Ida5e3d76133f6ed82c2bd49ca1599a0948914aa1

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=d1d60eb

[Jason Glasgow, 2011-01-05 16:48:36]

LGTM