Adding unit tests for profiler's stack tracer.

src/log.h

Index: src/log.h
diff --git a/src/log.h b/src/log.h
index 7d17567e12002ee1dd1c09f3bb210dfd233d53fd..8f60173117dd09838c300db5489f6ebca13da318 100644
--- a/src/log.h
+++ b/src/log.h
@@ -272,6 +272,17 @@ class Logger {
 };
 
 
+// Class that extracts stack trace, used for profiling
+class StackTracer BASE_EMBEDDED {
+ public:
+  StackTracer(unsigned int low_stack_bound): low_stack_bound_(low_stack_bound) {
+  }
+  void Trace(TickSample* sample);
+ private:
+  unsigned int low_stack_bound_;
+};
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_LOG_H_