Constant fold after inlining.

- Inlining opens up new opportunities for constant folding.
- Fix a bug in constant folder where the result type was not
  correctly set for the folding of a HCompare.
- Improve graph checker's coverage.

Change-Id: I0943bf8ff65505c4addc4a555a526b55e00b5268
diff --git a/compiler/optimizing/graph_checker.h b/compiler/optimizing/graph_checker.h
index ba60cb9..ae1557b 100644
--- a/compiler/optimizing/graph_checker.h
+++ b/compiler/optimizing/graph_checker.h
@@ -101,6 +101,7 @@
   void VisitPhi(HPhi* phi) OVERRIDE;
   void VisitBinaryOperation(HBinaryOperation* op) OVERRIDE;
   void VisitCondition(HCondition* op) OVERRIDE;
+  void VisitIf(HIf* instruction) OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SSAChecker);