Address review comments from a previous CL.

vm/snapshot.cc

Index: vm/snapshot.cc
===================================================================
--- vm/snapshot.cc	(revision 9828)
+++ vm/snapshot.cc	(working copy)
@@ -23,21 +23,22 @@
 
 
 static bool IsSingletonClassId(intptr_t index) {
-  // Check if this is a singleton object class which is shared by all isolates.
-  return (index >= Object::kClassClass && index < Object::kMaxId);
+  // Check if this is a singleton class which is shared by all isolates.
+  return ((index >= kClass && index <= kUnwindError) ||
+          (index >= kNullClassId && index <= kVoidClassId));
 }
 
 
 static bool IsObjectStoreClassId(intptr_t index) {
   // Check if this is a class which is stored in the object store.
-  return (index >= ObjectStore::kObjectClass && index < ObjectStore::kMaxId);
+  return ((index == kObject) || (index >= kInstance && index <= kJSRegExp));
 }
 
 
 static bool IsObjectStoreTypeId(intptr_t index) {
   // Check if this is a type which is stored in the object store.
   return (index >= ObjectStore::kObjectType &&
-          index <= ObjectStore::kListInterface);
+          index <= ObjectStore::kByteArrayInterface);
 }
 
 
@@ -474,10 +475,9 @@
   // stored in the object store.
   if (header_type == kObjectId) {
     intptr_t header_value = SerializedHeaderData::decode(class_header);
-    if (IsObjectStoreClassId(header_value)) {
-      return object_store()->GetClass(header_value);
-    } else if (IsSingletonClassId(header_value)) {
-      return Object::GetSingletonClass(header_value);  // return the singleton.
+    if (IsObjectStoreClassId(header_value) ||
+        IsSingletonClassId(header_value)) {
+      return class_table()->At(header_value);
     }
   }
   return Class::null();
@@ -518,10 +518,8 @@
   if (object_id == Object::kSentinelObject) {
     return Object::sentinel();
   }
-  if (IsSingletonClassId(object_id)) {
-    return Object::GetSingletonClass(object_id);  // return singleton object.
-  } else if (IsObjectStoreClassId(object_id)) {
-    return object_store()->GetClass(object_id);
+  if (IsSingletonClassId(object_id) || IsObjectStoreClassId(object_id)) {
+    return class_table()->At(object_id);
   } else if (object_id == ObjectStore::kTrueValue) {
     return object_store()->true_value();
   } else if (object_id == ObjectStore::kFalseValue) {
@@ -669,7 +667,7 @@
     WriteSerializationMarker(kInlined, object_id);
 
     // Write out the class information.
-    WriteIndexedObject(ObjectStore::kArrayClass);
+    WriteIndexedObject(kArray);
 
     // Write out the length field.
     Write<RawObject*>(rawarray->ptr()->length_);
@@ -689,7 +687,7 @@
     WriteSerializationMarker(kInlined, object_id);
 
     // Write out the class information.
-    WriteIndexedObject(ObjectStore::kImmutableArrayClass);
+    WriteIndexedObject(kImmutableArray);
 
     // Write out the length field.
     Write<RawObject*>(rawarray->ptr()->length_);
@@ -801,8 +799,7 @@
 
   // Check if it is a singleton class object which is shared by
   // all isolates.
-  RawClass* raw_class = reinterpret_cast<RawClass*>(rawobj);
-  intptr_t index = Object::GetSingletonClassIndex(raw_class);
+  intptr_t index = Object::GetSingletonClassIndex(rawobj);
   if (index != Object::kInvalidIndex) {
     WriteIndexedObject(index);
     return true;
@@ -948,14 +945,14 @@
 
 void SnapshotWriter::WriteClassId(RawClass* cls) {
   ASSERT(kind_ != Snapshot::kFull);
-  int id = object_store()->GetClassIndex(cls);
+  int id = cls->ptr()->id_;
   if (IsSingletonClassId(id) || IsObjectStoreClassId(id)) {
     WriteIndexedObject(id);
   } else {
     // TODO(5411462): Should restrict this to only core-lib classes in this
     // case.
     // Write out the class and tags information.
-    WriteObjectHeader(Object::kClassClass, GetObjectTags(cls));
+    WriteObjectHeader(kClass, GetObjectTags(cls));
 
     // Write out the library url and class name.
     RawLibrary* library = cls->ptr()->library_;