Cache number of type arguments in class object instead of recalculating it.

runtime/vm/raw_object_snapshot.cc

Index: runtime/vm/raw_object_snapshot.cc
===================================================================
--- runtime/vm/raw_object_snapshot.cc	(revision 28616)
+++ runtime/vm/raw_object_snapshot.cc	(working copy)
@@ -66,7 +66,9 @@
       cls.set_next_field_offset_in_words(reader->ReadIntptrValue());
     }
     cls.set_type_arguments_field_offset_in_words(reader->ReadIntptrValue());
-    cls.set_num_native_fields(reader->ReadIntptrValue());
+    cls.set_num_type_arguments(reader->Read<int16_t>());
+    cls.set_num_own_type_arguments(reader->Read<int16_t>());
+    cls.set_num_native_fields(reader->Read<uint16_t>());
     cls.set_token_pos(reader->ReadIntptrValue());
     cls.set_state_bits(reader->Read<uint16_t>());
 
@@ -111,7 +113,9 @@
       writer->WriteIntptrValue(ptr()->next_field_offset_in_words_);
     }
     writer->WriteIntptrValue(ptr()->type_arguments_field_offset_in_words_);
-    writer->WriteIntptrValue(ptr()->num_native_fields_);
+    writer->Write<int16_t>(ptr()->num_type_arguments_);
+    writer->Write<int16_t>(ptr()->num_own_type_arguments_);
+    writer->Write<uint16_t>(ptr()->num_native_fields_);
     writer->WriteIntptrValue(ptr()->token_pos_);
     writer->Write<uint16_t>(ptr()->state_bits_);