First steps toward a two stages new compiler.

runtime/vm/flow_graph_compiler_x64.h

Index: runtime/vm/flow_graph_compiler_x64.h
===================================================================
--- runtime/vm/flow_graph_compiler_x64.h	(revision 7399)
+++ runtime/vm/flow_graph_compiler_x64.h	(working copy)
@@ -25,7 +25,8 @@
  public:
   FlowGraphCompiler(Assembler* assembler,
                     const ParsedFunction& parsed_function,
-                    const GrowableArray<BlockEntryInstr*>& block_order);
+                    const GrowableArray<BlockEntryInstr*>& block_order,
+                    bool is_optimizing);
 
   virtual ~FlowGraphCompiler();
 
@@ -47,6 +48,8 @@
 
   BlockEntryInstr* current_block() const { return current_block_; }
 
+  bool is_optimizing() const { return is_optimizing_; }
+
   // Bail out of the flow graph compiler.  Does not return to the caller.
   void Bailout(const char* reason);
 
@@ -134,6 +137,7 @@
   BlockEntryInstr* current_block_;
   DescriptorList* pc_descriptors_list_;
   ExceptionHandlerList* exception_handlers_list_;
+  const bool is_optimizing_;
 
   DISALLOW_COPY_AND_ASSIGN(FlowGraphCompiler);
 };