Add basic C++ implementation of CPU profiler.

src/handles.h

Index: src/handles.h
diff --git a/src/handles.h b/src/handles.h
index 0c137a4ce7caa64a8bb4870a69376e58328e4a5a..f241da203675ab728d44559d6ce6fa2b52eb0d41 100644
--- a/src/handles.h
+++ b/src/handles.h
@@ -267,6 +267,8 @@ Handle<JSValue> GetScriptWrapper(Handle<Script> script);
 // Script line number computations.
 void InitScriptLineEnds(Handle<Script> script);
 int GetScriptLineNumber(Handle<Script> script, int code_position);
+// The safe version does not make heap allocations but may work much slower.
+int GetScriptLineNumberSafe(Handle<Script> script, int code_position);
 
 // Computes the enumerable keys from interceptors. Used for debug mirrors and
 // by GetKeysInFixedArrayFor below.