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

runtime/vm/trace_buffer_test.cc

 // 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.
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 #include "vm/json_stream.h"
 #include "vm/trace_buffer.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
-
-UNIT_TEST_CASE(TraceBufferEmpty) {
-  TraceBuffer* trace_buffer = new TraceBuffer(3);
+TEST_CASE(TraceBufferEmpty) {
+  Isolate* isolate = Isolate::Current();
+  TraceBuffer::Init(isolate, 3);
+  TraceBuffer* trace_buffer = isolate->trace_buffer();
   {
     JSONStream js;
     trace_buffer->PrintToJSONStream(&js);
     EXPECT_STREQ("{\"type\":\"TraceBuffer\",\"members\":[]}", js.ToCString());
   }
   delete trace_buffer;
 }
 
 
-UNIT_TEST_CASE(TraceBufferClear) {
-  TraceBuffer* trace_buffer = new TraceBuffer(3);
+TEST_CASE(TraceBufferClear) {
+  Isolate* isolate = Isolate::Current();
+  TraceBuffer::Init(isolate, 3);
+  TraceBuffer* trace_buffer = isolate->trace_buffer();
   trace_buffer->Trace(kMicrosecondsPerSecond * 1, "abc");
   trace_buffer->Clear();
   {
     JSONStream js;
     trace_buffer->PrintToJSONStream(&js);
     EXPECT_STREQ("{\"type\":\"TraceBuffer\",\"members\":[]}", js.ToCString());
   }
   delete trace_buffer;
 }
 
 
-UNIT_TEST_CASE(TraceBufferTrace) {
-  TraceBuffer* trace_buffer = new TraceBuffer(3);
+TEST_CASE(TraceBufferTrace) {
+  Isolate* isolate = Isolate::Current();
+  TraceBuffer::Init(isolate, 3);
+  TraceBuffer* trace_buffer = isolate->trace_buffer();
 
   trace_buffer->Trace(kMicrosecondsPerSecond * 1, "abc");
   {
     JSONStream js;
     trace_buffer->PrintToJSONStream(&js);
     EXPECT_STREQ("{\"type\":\"TraceBuffer\",\"members\":["
                  "{\"type\":\"TraceBufferEntry\",\"time\":1.000000,"
                  "\"message\":\"abc\"}]}", js.ToCString());
   }
   trace_buffer->Trace(kMicrosecondsPerSecond * 2, "def");
@@ skipping 28 matching lines @@
                  "\"message\":\"def\"},"
                  "{\"type\":\"TraceBufferEntry\",\"time\":3.000000,"
                  "\"message\":\"ghi\"},"
                  "{\"type\":\"TraceBufferEntry\",\"time\":4.000000,"
                  "\"message\":\"jkl\"}]}", js.ToCString());
   }
   delete trace_buffer;
 }
 
 
-UNIT_TEST_CASE(TraceBufferTraceF) {
-  TraceBuffer* trace_buffer = new TraceBuffer(3);
+TEST_CASE(TraceBufferTraceF) {
+  Isolate* isolate = Isolate::Current();
+  TraceBuffer::Init(isolate, 3);
+  TraceBuffer* trace_buffer = isolate->trace_buffer();
   trace_buffer->TraceF("foo %d %s", 99, "bar");
   {
     JSONStream js;
     trace_buffer->PrintToJSONStream(&js);
     EXPECT_SUBSTRING("foo 99 bar", js.ToCString());
   }
   delete trace_buffer;
 }
 
 
 }  // namespace dart