Avoid manual object's body traversal in GC.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 12f220f144c2214e1b7695d0c749ae64cad55f17..e5865b788625ef727231c40a39e6f0f11f2372c1 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1504,13 +1504,6 @@ class MapWord BASE_EMBEDDED {
 };
 
 
-// The content of an heap object (except for the map pointer). kTaggedValues
-// objects can contain both heap pointers and Smis, kMixedValues can contain
-// heap pointers, Smis, and raw values (e.g. doubles or strings), and kRawValues
-// objects can contain raw values and Smis.
-enum class HeapObjectContents { kTaggedValues, kMixedValues, kRawValues };
-
-
 // HeapObject is the superclass for all classes describing heap allocated
 // objects.
 class HeapObject: public Object {
@@ -1587,9 +1580,6 @@ class HeapObject: public Object {
   // Returns the heap object's size in bytes
   inline int Size();
 
-  // Indicates what type of values this heap object may contain.
-  inline HeapObjectContents ContentType();
-
   // Given a heap object's map pointer, returns the heap size in bytes
   // Useful when the map pointer field is used for other purposes.
   // GC internal.