What is this plant?

There are two unidentified trees on the lot with deep bronzy leaves year round. Maybe some sort of plum-type-thing? Anyone got any guesses?

UPDATE From my dad's friend:
"My guess is that it is the purple form of the Myrobalan plum (Prunus cerasifera var. either "Pissardii" or "nigra".) If it is that, it should flower in late winter/very early spring (earlier than blackthorn), but who knows in San Fransisco! With any luck it should produce fruit about 2cm diam, rather sour raw but make good pies. "