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

src/log-utils.h

 // Copyright 2006-2009 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.
 
 #ifndef V8_LOG_UTILS_H_
 #define V8_LOG_UTILS_H_
 
+#include <string>
+
 #include "src/allocation.h"
 
 namespace v8 {
 namespace internal {
 
 class Logger;
 
 // Functions and data for performing output of log messages.
 class Log {
  public:
@@ skipping 55 matching lines @@
     // Appends an address.
     void AppendAddress(Address addr);
 
     void AppendSymbolName(Symbol* symbol);
 
     void AppendDetailed(String* str, bool show_impl_info);
 
     // Append a portion of a string.
     void AppendStringPart(const char* str, int len);
 
+    // GetSubstring fills str with a string consisting
+    // all that's been appendend starting from a call to
+    // StartSubstring and till a call to EndSubstring
+    void StartSubstring();
+    void EndSubstring();
+    void GetSubstring(std::string* str);
+
     // Write the log message to the log file currently opened.
     void WriteToLogFile();
 
    private:
     Log* log_;
     base::LockGuard<base::Mutex> lock_guard_;
     int pos_;
+    int substr_start_pos_;
+    int substr_end_pos_;
   };
 
  private:
   explicit Log(Logger* logger);
 
   // Opens stdout for logging.
   void OpenStdout();
 
   // Opens file for logging.
   void OpenFile(const char* name);
@@ skipping 28 matching lines @@
 
   Logger* logger_;
 
   friend class Logger;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_LOG_UTILS_H_