Reclaim the CreatedFromSnapshot bit and use it to indicate VM Heap object

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
diff --git a/runtime/vm/snapshot.cc b/runtime/vm/snapshot.cc
index b08e704d7b220ad08c1691e7c49f3b2a7c169cbb..907e80577cda45b0eb934896f60799a8b8a7852d 100644
--- a/runtime/vm/snapshot.cc
+++ b/runtime/vm/snapshot.cc
@@ -325,6 +325,11 @@ RawObject* SnapshotReader::VmIsolateSnapshotObject(intptr_t index) const {
 }
 
 
+bool SnapshotReader::is_vm_isolate() const {
+  return isolate_ == Dart::vm_isolate();
+}
+
+
 RawObject* SnapshotReader::ReadObjectImpl(bool as_reference,
                                           intptr_t patch_object_id,
                                           intptr_t patch_offset) {
@@ -463,9 +468,6 @@ RawObject* SnapshotReader::ReadObjectRef(intptr_t object_id,
 #undef SNAPSHOT_READ
     default: UNREACHABLE(); break;
   }
-  if (kind_ == Snapshot::kFull) {
-    pobj_.SetCreatedFromSnapshot();
-  }
   return pobj_.raw();
 }
 
@@ -536,10 +538,14 @@ RawObject* SnapshotReader::ReadInlinedObject(intptr_t object_id,
         result->SetFieldAtOffset(offset, Object::null_object());
         offset += kWordSize;
       }
-      result->SetCreatedFromSnapshot();
-    } else if (RawObject::IsCanonical(tags)) {
-      *result = result->CheckAndCanonicalize(NULL);
-      ASSERT(!result->IsNull());
+    }
+    if (RawObject::IsCanonical(tags)) {
+      if (kind_ == Snapshot::kFull) {
+        result->SetCanonical();
+      } else {
+        *result = result->CheckAndCanonicalize(NULL);
+        ASSERT(!result->IsNull());
+      }
     }
     return result->raw();
   } else if (header_id == kStaticImplicitClosureObjectId) {
@@ -578,9 +584,6 @@ RawObject* SnapshotReader::ReadInlinedObject(intptr_t object_id,
 #undef SNAPSHOT_READ
     default: UNREACHABLE(); break;
   }
-  if (kind_ == Snapshot::kFull) {
-    pobj_.SetCreatedFromSnapshot();
-  }
   AddPatchRecord(object_id, patch_object_id, patch_offset);
   return pobj_.raw();
 }
@@ -1071,6 +1074,7 @@ RawObject* SnapshotReader::AllocateUninitialized(intptr_t class_id,
   ASSERT(class_id != kIllegalCid);
   tags = RawObject::ClassIdTag::update(class_id, tags);
   tags = RawObject::SizeTag::update(size, tags);
+  tags = RawObject::VMHeapObjectTag::update(is_vm_isolate(), tags);
   raw_obj->ptr()->tags_ = tags;
   return raw_obj;
 }
@@ -1209,9 +1213,6 @@ void SnapshotReader::ArrayReadFrom(intptr_t object_id,
                                    const Array& result,
                                    intptr_t len,
                                    intptr_t tags) {
-  // Set the object tags.
-  result.set_tags(tags);
-
   // Setup the object fields.
   const intptr_t typeargs_offset =
       GrowableObjectArray::type_arguments_offset() / kWordSize;
@@ -2053,11 +2054,6 @@ void SnapshotWriter::WriteClassId(RawClass* cls) {
   ASSERT(kind_ != Snapshot::kFull);
   int class_id = cls->ptr()->id_;
   ASSERT(!IsSingletonClassId(class_id) && !IsObjectStoreClassId(class_id));
-  // TODO(5411462): Should restrict this to only core-lib classes in this
-  // case.
-  // Write out the class and tags information.
-  WriteVMIsolateObject(kClassCid);
-  WriteTags(GetObjectTags(cls));
 
   // Write out the library url and class name.
   RawLibrary* library = cls->ptr()->library_;