ART: Address late comments on a GVN memory-saving CL

Added extra comments and removed redundant code as requested.

Bug: 28173563
Bug: 28287086

Change-Id: If6aff68c4c30427a86a27ffba5df1ae135edd294
(cherry picked from commit 94408d3144061bd6efc74b3d884d38169969c63f)
1 file changed