new compilerplugin returnbyref

Find places where we are returning a pointer to something, where we can
be returning a reference.
e.g.
   class A {
     struct X x;
     public X* getX() { return &x; }
   }
which can be:
     public X& getX() { return x; }

Change-Id: I796fd23fd36a18aedf6e36bc28f8fab4f518c6c7