Further improve type optimization reusing the type argument vector of the

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 22154)
+++ runtime/vm/object.h	(working copy)
@@ -1024,6 +1024,8 @@
   virtual bool IsResolved() const;
   virtual bool IsInstantiated() const;
   virtual bool IsUninstantiatedIdentity() const;
+  virtual bool CanShareInstantiatorTypeArguments(
+      const Class& instantiator_class) const;
   virtual bool IsBounded() const;
 
   virtual intptr_t Hash() const;
@@ -1067,6 +1069,8 @@
   virtual bool IsResolved() const;
   virtual bool IsInstantiated() const;
   virtual bool IsUninstantiatedIdentity() const;
+  virtual bool CanShareInstantiatorTypeArguments(
+      const Class& instantiator_class) const;
   virtual bool IsBounded() const;
   // Canonicalize only if instantiated, otherwise returns 'this'.
   virtual RawAbstractTypeArguments* Canonicalize() const;
@@ -1123,7 +1127,15 @@
   virtual void SetTypeAt(intptr_t index, const AbstractType& value) const;
   virtual bool IsResolved() const { return true; }
   virtual bool IsInstantiated() const { return true; }
-  virtual bool IsUninstantiatedIdentity() const  { return false; }
+  virtual bool IsUninstantiatedIdentity() const {
+    UNREACHABLE();
+    return false;
+  }
+  virtual bool CanShareInstantiatorTypeArguments(
+      const Class& instantiator_class) const {
+    UNREACHABLE();
+    return false;
+  }
   virtual bool IsBounded() const { return false; }  // Bounds were checked.
 
   RawAbstractTypeArguments* uninstantiated_type_arguments() const {