[WIP] A sampler thread in d8 for consuming the new API.

src/log-utils.cc

 // Copyright 2009 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/v8.h"
 
 #include "src/log-utils.h"
 #include "src/string-stream.h"
 
 namespace v8 {
@@ skipping 199 matching lines @@
     if (len == 0) return;
   }
   Vector<char> buf(log_->message_buffer_ + pos_,
                    Log::kMessageBufferSize - pos_);
   StrNCpy(buf, str, len);
   pos_ += len;
   ASSERT(pos_ <= Log::kMessageBufferSize);
 }
 
 
+void Log::MessageBuilder::StartSubstring() {
+  substr_start_pos_ = pos_;
+}
+
+
+void Log::MessageBuilder::EndSubstring() {
+  substr_end_pos_ = pos_;
+}
+
+
+void Log::MessageBuilder::GetSubstring(std::string* str) {
+  ASSERT_EQ(0, str->size());
+  str->append(log_->message_buffer_ + substr_start_pos_,
+              substr_end_pos_ - substr_start_pos_);
+}
+
+
 void Log::MessageBuilder::WriteToLogFile() {
   ASSERT(pos_ <= Log::kMessageBufferSize);
   const int written = log_->WriteToFile(log_->message_buffer_, pos_);
   if (written != pos_) {
     log_->stop();
     log_->logger_->LogFailure();
   }
 }
 
 
 } }  // namespace v8::internal