Fix another case where loop-convert wasn't handling correctly data members.
If the container expression was obtained from the point where "size" (which usually is a const method) is invoked, then the topmost node in this expression may be an implicit cast to const.
When the container is a data member, the check was trying to obtain the member expression directly and was failing in the case mentioned above. This is solved by ignoring implicit casts.
Subscribers: cfe-commits, alexfh
Differential Revision: http://reviews.llvm.org/D14378