[Tracing] Remove unnecessary memory allocation in runtime call stats.

src/counters.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/counters.h"
 
 #include <iomanip>
 
 #include "src/base/platform/platform.h"
 #include "src/isolate.h"
@@ skipping 346 matching lines @@
   FOR_EACH_API_COUNTER(RESET_COUNTER)
 #undef RESET_COUNTER
 
 #define RESET_COUNTER(name) this->Handler_##name.Reset();
   FOR_EACH_HANDLER_COUNTER(RESET_COUNTER)
 #undef RESET_COUNTER
 
   in_use_ = true;
 }
 
-const char* RuntimeCallStats::Dump() {
+std::string RuntimeCallStats::Dump() {
   buffer_.str(std::string());
   buffer_.clear();
   buffer_ << "{";
 #define DUMP_COUNTER(name) \
   if (this->name.count > 0) this->name.Dump(buffer_);
   FOR_EACH_MANUAL_COUNTER(DUMP_COUNTER)
 #undef DUMP_COUNTER
 
 #define DUMP_COUNTER(name, nargs, result_size) \
   if (this->Runtime_##name.count > 0) this->Runtime_##name.Dump(buffer_);
   FOR_EACH_INTRINSIC(DUMP_COUNTER)
 #undef DUMP_COUNTER
 
 #define DUMP_COUNTER(name) \
   if (this->Builtin_##name.count > 0) this->Builtin_##name.Dump(buffer_);
   BUILTIN_LIST_C(DUMP_COUNTER)
 #undef DUMP_COUNTER
 
 #define DUMP_COUNTER(name) \
   if (this->API_##name.count > 0) this->API_##name.Dump(buffer_);
   FOR_EACH_API_COUNTER(DUMP_COUNTER)
 #undef DUMP_COUNTER
 
 #define DUMP_COUNTER(name) \
   if (this->Handler_##name.count > 0) this->Handler_##name.Dump(buffer_);
   FOR_EACH_HANDLER_COUNTER(DUMP_COUNTER)
 #undef DUMP_COUNTER
   buffer_ << "\"END\":[]}";
-  const std::string& buffer_str = buffer_.str();
-  size_t length = buffer_str.size();
-  if (length > len_) {
-    buffer_c_str_.reset(new char[length + 1]);
-    len_ = length;
-  }
-  strncpy(buffer_c_str_.get(), buffer_str.c_str(), length + 1);
   in_use_ = false;
-  return buffer_c_str_.get();
+  return buffer_.str();
 }
 
 }  // namespace internal
 }  // namespace v8