Use ParametrizedType instead of Type where appropriate. Expand ToCString of type related classes.

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
===================================================================
--- runtime/vm/snapshot.cc	(revision 1937)
+++ runtime/vm/snapshot.cc	(working copy)
@@ -286,7 +286,8 @@
 
   // Check if classes are not being serialized and it is preinitialized type.
   if (!serialize_classes_) {
-    RawType* raw_type = reinterpret_cast<RawType*>(rawobj);
+    RawParameterizedType* raw_type =
+        reinterpret_cast<RawParameterizedType*>(rawobj);
     index = object_store()->GetTypeIndex(raw_type);
     if (index != ObjectStore::kInvalidIndex) {
       WriteObjectHeader(kObjectId, index);