[WIP]Create a V8 sampler library and tracing controller.

src/log.h

Index: src/log.h
diff --git a/src/log.h b/src/log.h
index 1a454dad264c176afff79a193bdf614eb7f52a8b..139ac5bce74eaeb997e049974165b05284965d5a 100644
--- a/src/log.h
+++ b/src/log.h
@@ -14,6 +14,8 @@
 
 namespace v8 {
 
+class V8Sampler;
+
 namespace base {
 class Semaphore;
 }
@@ -146,7 +148,7 @@ struct TickSample;
 class JitLogger;
 class PerfBasicLogger;
 class LowLevelLogger;
-class Sampler;
+// class Sampler;
 
 class Logger {
  public:
@@ -166,7 +168,8 @@ class Logger {
   void SetCodeEventHandler(uint32_t options,
                            JitCodeEventHandler event_handler);
 
-  Sampler* sampler();
+  //Sampler* sampler();
+  V8Sampler* sampler();
 
   // Frees resources acquired in SetUp.
   // When a temporary file is used for the log, returns its stream descriptor,