ART: ChildBlockIterator Implementation

- Added the API to be able to walk through a BasicBlock's children directly.
- When calling Reset(GrowableArray*), there is an assignment to the g_list_
    member. This is not possible with the g_list_ being const.

Change-Id: I25d06484fd93848d80ccf96a1324058370b2ee46
Signed-Off-By: Jean Christophe Beyler <jean.christophe.beyler@intel.com>
Signed-off-by: Razvan A Lupusoru <razvan.a.lupusoru@intel.com>
Signed-off-by: Yixin Shou <yixin.shou@intel.com>
Signed-off-by: Chao-ying Fu <chao-ying.fu@intel.com>
Signed-off-by: Udayan Banerji <udayan.banerji@intel.com>