Reduce the number of captured variables in async code, by only capturing local

runtime/vm/ast_transformer.h

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_AST_TRANSFORMER_H_
 #define VM_AST_TRANSFORMER_H_
 
 #include "platform/assert.h"
 #include "vm/ast.h"
 
@@ skipping 21 matching lines @@
 //   :result_param = t_1;
 //   <continuation logic>
 //   t_2 = :result_param;
 //   t_3 = foo();
 //   t_4 = t_2.operator+(t_3);
 //
 // and a resulting expression of a load of t_4.
 //
 class AwaitTransformer : public AstNodeVisitor {
  public:
-  AwaitTransformer(SequenceNode* preamble, LocalScope* function_top);
+  AwaitTransformer(SequenceNode* preamble, LocalScope* async_temp_scope);
 
 #define DECLARE_VISIT(BaseName)                                                \
   virtual void Visit##BaseName##Node(BaseName##Node* node);
 
   FOR_EACH_NODE(DECLARE_VISIT)
 #undef DECLARE_VISIT
 
   AstNode* Transform(AstNode* expr);
 
  private:
   LocalVariable* EnsureCurrentTempVar();
   LocalVariable* AddToPreambleNewTempVar(AstNode* node);
   ArgumentListNode* TransformArguments(ArgumentListNode* node);
   AstNode* LazyTransform(const Token::Kind kind,
                          AstNode* new_left,
                          AstNode* right);
   LocalScope* ChainNewScope(LocalScope* parent);
   LocalVariable* GetVariableInScope(LocalScope* scope, const String& symbol);
 
   void NextTempVar() { temp_cnt_++; }
 
   Thread* thread() const { return thread_; }
 
   SequenceNode* preamble_;
   int32_t temp_cnt_;
   AstNode* result_;
-  LocalScope* function_top_;
+  LocalScope* async_temp_scope_;
 
   Thread* thread_;
 
   DISALLOW_COPY_AND_ASSIGN(AwaitTransformer);
 };
 
 }  // namespace dart
 
 #endif  // VM_AST_TRANSFORMER_H_