Use the instruction iterator rather than an explicit loop in more places.

runtime/vm/flow_graph_optimizer.h

Index: runtime/vm/flow_graph_optimizer.h
diff --git a/runtime/vm/flow_graph_optimizer.h b/runtime/vm/flow_graph_optimizer.h
index fe1a77951d7f943f09b16ab87cd6254ea8459f04..b33a4b1069afef5d0cc4733a5c324a0daa6b8549 100644
--- a/runtime/vm/flow_graph_optimizer.h
+++ b/runtime/vm/flow_graph_optimizer.h
@@ -33,8 +33,6 @@ class FlowGraphOptimizer : public FlowGraphVisitor {
   virtual void VisitBind(BindInstr* instr);
 
  private:
-  void VisitBlocks();
-
   bool TryReplaceWithBinaryOp(BindInstr* instr,
                               InstanceCallComp* comp,
                               Token::Kind op_kind);
@@ -56,7 +54,8 @@ class FlowGraphOptimizer : public FlowGraphVisitor {
 // method, i.e., does not contain any calls to runtime or other Dart code.
 class FlowGraphAnalyzer : public ValueObject {
  public:
-  explicit FlowGraphAnalyzer(const GrowableArray<BlockEntryInstr*>& blocks);
+  explicit FlowGraphAnalyzer(const GrowableArray<BlockEntryInstr*>& blocks)
+      : blocks_(blocks), is_leaf_(false) {}
   virtual ~FlowGraphAnalyzer() {}
 
   void Analyze();