Refactor VMTagScope to Thread* rather than Isolate*.

runtime/vm/parser.h

 // Copyright (c) 2012, 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_PARSER_H_
 #define VM_PARSER_H_
 
 #include "include/dart_api.h"
 
 #include "platform/assert.h"
@@ skipping 132 matching lines @@
     return (num_copied_params_ == 0)
         ? function().num_fixed_parameters() : 0;
   }
 
   void AllocateVariables();
   void AllocateIrregexpVariables(intptr_t num_stack_locals);
 
   void record_await() { have_seen_await_expr_ = true; }
   bool have_seen_await() const { return have_seen_await_expr_; }
 
+  Thread* thread() const { return thread_; }
   Isolate* isolate() const { return thread_->isolate(); }
   Zone* zone() const { return thread_->zone(); }
 
  private:
   Thread* thread_;
   const Function& function_;
   Code& code_;
   SequenceNode* node_sequence_;
   RegExpCompileData* regexp_compile_data_;
   LocalVariable* instantiator_;
@@ skipping 717 matching lines @@
 
   // Indentation of parser trace.
   intptr_t trace_indent_;
 
   DISALLOW_COPY_AND_ASSIGN(Parser);
 };
 
 }  // namespace dart
 
 #endif  // VM_PARSER_H_