Implement default traversals in CFG & SSA graph checkers.

- Check CFG graphs using an insertion order traversal.
- Check SSA form graphs using a reverse post-order traversal.

Change-Id: Ib9062599bdbf3c17b9f213b743274b2d71a9fa90
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index a058dea..aee2177 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -553,6 +553,12 @@
   }
 }
 
+void HGraphVisitor::VisitReversePostOrder() {
+  for (HReversePostOrderIterator it(*graph_); !it.Done(); it.Advance()) {
+    VisitBasicBlock(it.Current());
+  }
+}
+
 void HGraphVisitor::VisitBasicBlock(HBasicBlock* block) {
   for (HInstructionIterator it(block->GetPhis()); !it.Done(); it.Advance()) {
     it.Current()->Accept(this);