VM: Use BlockIterator in the optimizer consistently for iterating the flow graph

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index 886a2f5977fc2c353098a984722f62bd755456df..a6d8a0f3be477c0e52f02a02762291e39d84ee59 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -8173,7 +8173,7 @@ class Environment : public ZoneAllocated {
 class FlowGraphVisitor : public ValueObject {
  public:
   explicit FlowGraphVisitor(const GrowableArray<BlockEntryInstr*>& block_order)
-      : block_order_(block_order), current_iterator_(NULL) { }
+      : current_iterator_(NULL), block_order_(block_order) { }
   virtual ~FlowGraphVisitor() { }
 
   ForwardInstructionIterator* current_iterator() const {
@@ -8194,10 +8194,10 @@ class FlowGraphVisitor : public ValueObject {
 #undef DECLARE_VISIT_INSTRUCTION
 
  protected:
-  const GrowableArray<BlockEntryInstr*>& block_order_;
   ForwardInstructionIterator* current_iterator_;
 
  private:
+  const GrowableArray<BlockEntryInstr*>& block_order_;
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };