Incomplete type hierarchy when using method reference

See: https://bugs.eclipse.org/bugs/show_bug.cgi?id=560545

To reproduce, compute the type hierarchy of `TestInterface` in the following snippet:

```
public class TestClass {

interface TestInterface {
void testMethod();
}

public TestInterface ti1 = TestClass.this::testMethod;
public TestInterface ti2 = () -> testMethod();
public TestInterface ti3 = new TestInterface() {
public void testMethod() {
TestClass.this.testMethod();
}
};

public void testMethod() {
System.out.println("TestClass.testMethod()");
}

public static void main(String[] args) {
TestClass t = new TestClass();
t.ti1.testMethod();
t.ti2.testMethod();
t.ti3.testMethod();
}
}
```

Observe that no implementer is found for the method reference. Only for the lambda and the anonymous type.