ART: Same skip-compilation heuristic in both backends

When deciding if a method should be compiled, Optimizing counts the
DEX instructions while Quick approximates this figure as the size of
the CodeItem. This patch modifies Optimizing to use the same logic
so that the two backends reject the same set of methods.

Change-Id: Icb12bf2977f948198df08d59f243532ec8c61783