Introduce simple Thread class to support gradual refactoring of interfaces.

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"
 
 namespace dart {
 
 class ParsedFunction;
+class Thread;
 
 // Translate an AstNode containing an expression (that itself contains one or
 // more awaits) into a sequential representation where subexpressions are
 // evaluated sequentially into intermediates. Those intermediates are stored
 // within a context.
 //
 // This allows a function to be suspended and resumed from within evaluating an
 // expression. The evaluation is split among a so-called preamble and the
 // evaluation of the resulting expression (which is only a single load).
 //
@@ skipping 32 matching lines @@
   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_++; }
 
-  Isolate* isolate() const { return isolate_; }
+  Thread* thread() const { return thread_; }
 
   SequenceNode* preamble_;
   int32_t temp_cnt_;
   AstNode* result_;
   ParsedFunction* const parsed_function_;
   LocalScope* function_top_;
 
-  Isolate* isolate_;
+  Thread* thread_;
 
   DISALLOW_COPY_AND_ASSIGN(AwaitTransformer);
 };
 
 }  // namespace dart
 
 #endif  // VM_AST_TRANSFORMER_H_