Implement type cast in the VM.

runtime/vm/flow_graph_builder.h

Index: runtime/vm/flow_graph_builder.h
===================================================================
--- runtime/vm/flow_graph_builder.h	(revision 9069)
+++ runtime/vm/flow_graph_builder.h	(working copy)
@@ -178,7 +178,8 @@
                                  Value** receiver,
                                  Value** value);
 
-  virtual void BuildInstanceOf(ComparisonNode* node);
+  virtual void BuildTypeTest(ComparisonNode* node);
+  virtual void BuildTypeCast(ComparisonNode* node);
 
   bool MustSaveRestoreContext(SequenceNode* node) const;
 
@@ -274,7 +275,8 @@
   virtual void CompiletimeStringInterpolation(const Function& interpol_func,
                                               const Array& literals);
 
-  virtual void BuildInstanceOf(ComparisonNode* node);
+  virtual void BuildTypeTest(ComparisonNode* node);
+  virtual void BuildTypeCast(ComparisonNode* node);
 };