ART: Implement HSelect

This patch adds a new HIR instruction to Optimizing. HSelect returns
one of two inputs based on the outcome of a condition.

This is only initial implementation which:
 - defines the new instruction,
 - repurposes BooleanSimplifier to emit it,
 - extends InstructionSimplifier to statically resolve it,
 - updates existing code and tests accordingly.

Code generators currently emit fallback if/then/else code and will be
updated in follow-up CLs to use platform-specific conditional moves
when possible.

Change-Id: Ib61b17146487ebe6b55350c2b589f0b971dcaaee
diff --git a/compiler/optimizing/graph_checker.h b/compiler/optimizing/graph_checker.h
index 2e16bfe..8724cde 100644
--- a/compiler/optimizing/graph_checker.h
+++ b/compiler/optimizing/graph_checker.h
@@ -126,6 +126,7 @@
   void VisitCondition(HCondition* op) OVERRIDE;
   void VisitIf(HIf* instruction) OVERRIDE;
   void VisitPackedSwitch(HPackedSwitch* instruction) OVERRIDE;
+  void VisitSelect(HSelect* instruction) OVERRIDE;
   void VisitBooleanNot(HBooleanNot* instruction) OVERRIDE;
   void VisitConstant(HConstant* instruction) OVERRIDE;
   void VisitBoundType(HBoundType* instruction) OVERRIDE;