Provide the isolate with a trace buffer, but do not allocate one by default.

runtime/vm/trace_buffer.h

 // Copyright (c) 2013, 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_TRACE_BUFFER_H_
 #define VM_TRACE_BUFFER_H_
 
 #include "platform/assert.h"
 #include "platform/globals.h"
 #include "vm/json_stream.h"
 
 namespace dart {
 
 class JSONStream;
 
 struct TraceBufferEntry {
   int64_t micros;
   char* message;
   bool empty() const {
     return message == NULL;
   }
 };
 
 class TraceBuffer {
  public:
   static const intptr_t kDefaultCapacity = 1024;
 
-  explicit TraceBuffer(intptr_t capacity = kDefaultCapacity);
+  static void Init(Isolate* isolate, intptr_t capacity = kDefaultCapacity);
+
   ~TraceBuffer();
 
   void Clear();
 
   // Internally message is copied.
   void Trace(int64_t micros, const char* message);
   // Internally message is copied.
   void Trace(const char* message);
   void TraceF(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
 
   void PrintToJSONStream(JSONStream* stream) const;
 
  private:
-  void Init();
+  TraceBuffer(Isolate* isolate, intptr_t capacity);
   void Cleanup();
   void Fill(TraceBufferEntry* entry, int64_t micros, char* msg);
   void AppendTrace(int64_t micros, char* message);
 
+  Isolate* isolate_;
   TraceBufferEntry* ring_;
   const intptr_t ring_capacity_;
   intptr_t ring_cursor_;
 
   intptr_t RingIndex(intptr_t i) const {
     return i % ring_capacity_;
   }
 
   DISALLOW_COPY_AND_ASSIGN(TraceBuffer);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_TRACE_BUFFER_H_