Reland "Precisely sweep scan on scavenge pages and use heap iterator to iterate over them."

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index d49e365e59e51823655a71dee8046452551c8040..3cdd70bf9d86222e7fbd5d726a457e62260bb44c 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -714,6 +714,7 @@ enum InstanceType {
   FIXED_UINT8_CLAMPED_ARRAY_TYPE,  // LAST_FIXED_TYPED_ARRAY_TYPE
 
   FIXED_DOUBLE_ARRAY_TYPE,
+  CONSTANT_POOL_ARRAY_TYPE,
   FILLER_TYPE,  // LAST_DATA_TYPE
 
   // Structs.
@@ -740,7 +741,6 @@ enum InstanceType {
   BREAK_POINT_INFO_TYPE,
 
   FIXED_ARRAY_TYPE,
-  CONSTANT_POOL_ARRAY_TYPE,
   SHARED_FUNCTION_INFO_TYPE,
 
   // All the following types are subtypes of JSReceiver, which corresponds to
@@ -1716,6 +1716,10 @@ class HeapObject: public Object {
   // Returns the heap object's size in bytes
   inline int Size();
 
+  // Returns true if this heap object contains only references to other
+  // heap objects.
+  inline bool ContainsPointers();
+
   // 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.