Add initial version of retainers heap profile.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 028dd11181a416616f387ed6ddde49a05b940a82..92602c8506b22dcedabe44637d0fc42a2e4e2a38 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -1443,20 +1443,6 @@ class DisableAssertNoAllocation {
 
 #endif
 
-#ifdef ENABLE_LOGGING_AND_PROFILING
-// The HeapProfiler writes data to the log files, which can be postprocessed
-// to generate .hp files for use by the GHC/Valgrind tool hp2ps.
-class HeapProfiler {
- public:
-  // Write a single heap sample to the log file.
-  static void WriteSample();
-
- private:
-  // Update the array info with stats from obj.
-  static void CollectStats(HeapObject* obj, HistogramInfo* info);
-};
-#endif
-
 // GCTracer collects and prints ONE line after each garbage collector
 // invocation IFF --trace_gc is used.