[heap] Decouple SpaceIterator from ObjectIterator.

src/heap/spaces.cc

Index: src/heap/spaces.cc
diff --git a/src/heap/spaces.cc b/src/heap/spaces.cc
index 8982a2953273abbe35993b57ab63ee43d42ae0d7..467f0c921602ba13c7e751ceecb1aa4b684ade59 100644
--- a/src/heap/spaces.cc
+++ b/src/heap/spaces.cc
@@ -1430,6 +1430,10 @@ void PagedSpace::ReleasePage(Page* page) {
   heap()->memory_allocator()->Free<MemoryAllocator::kPreFreeAndQueue>(page);
 }
 
+std::unique_ptr<ObjectIterator> PagedSpace::GetObjectIterator() {
+  return std::unique_ptr<ObjectIterator>(new HeapObjectIterator(this));
+}
+
 #ifdef DEBUG
 void PagedSpace::Print() {}
 #endif
@@ -1816,6 +1820,10 @@ void NewSpace::InlineAllocationStep(Address top, Address new_top,
   }
 }
 
+std::unique_ptr<ObjectIterator> NewSpace::GetObjectIterator() {
+  return std::unique_ptr<ObjectIterator>(new SemiSpaceIterator(this));
+}
+
 #ifdef VERIFY_HEAP
 // We do not use the SemiSpaceIterator because verification doesn't assume
 // that it works (it depends on the invariants we are checking).
@@ -2089,6 +2097,11 @@ void SemiSpace::set_age_mark(Address mark) {
   }
 }
 
+std::unique_ptr<ObjectIterator> SemiSpace::GetObjectIterator() {
+  // Use the NewSpace::NewObjectIterator to iterate the ToSpace.
+  UNREACHABLE();
+  return std::unique_ptr<ObjectIterator>();
+}
 
 #ifdef DEBUG
 void SemiSpace::Print() {}
@@ -3141,6 +3154,9 @@ bool LargeObjectSpace::Contains(HeapObject* object) {
   return owned;
 }
 
+std::unique_ptr<ObjectIterator> LargeObjectSpace::GetObjectIterator() {
+  return std::unique_ptr<ObjectIterator>(new LargeObjectIterator(this));
+}
 
 #ifdef VERIFY_HEAP
 // We do not assume that the large object iterator works, because it depends