Cleanup: use const reference for ParsedFunction where possible.

runtime/vm/flow_graph_compiler.h

Index: runtime/vm/flow_graph_compiler.h
===================================================================
--- runtime/vm/flow_graph_compiler.h	(revision 43213)
+++ runtime/vm/flow_graph_compiler.h	(working copy)
@@ -268,6 +268,7 @@
   FlowGraphCompiler(
       Assembler* assembler,
       FlowGraph* flow_graph,
+      const ParsedFunction& parsed_function,
       bool is_optimizing,
       const GrowableArray<const Function*>& inline_id_to_function);
 
@@ -280,7 +281,7 @@
 
   // Accessors.
   Assembler* assembler() const { return assembler_; }
-  ParsedFunction& parsed_function() const { return parsed_function_; }
+  const ParsedFunction& parsed_function() const { return parsed_function_; }
   const GrowableArray<BlockEntryInstr*>& block_order() const {
     return block_order_;
   }
@@ -634,7 +635,7 @@
 
   Isolate* isolate_;
   Assembler* assembler_;
-  ParsedFunction& parsed_function_;
+  const ParsedFunction& parsed_function_;
   const FlowGraph& flow_graph_;
   const GrowableArray<BlockEntryInstr*>& block_order_;