Do not ignore side effects of a type test or type cast as expression, such

runtime/vm/flow_graph_builder.h

Index: runtime/vm/flow_graph_builder.h
===================================================================
--- runtime/vm/flow_graph_builder.h	(revision 35282)
+++ runtime/vm/flow_graph_builder.h	(working copy)
@@ -434,6 +434,11 @@
  private:
   friend class TempLocalScope;  // For ReturnDefinition.
 
+  // Helper to drop the result value.
+  virtual void ReturnValue(Value* value) {
+    Do(new DropTempsInstr(0, value));
+  }
+
   // Specify a definition of the final result.  Adds the definition to
   // the graph, but normally overridden in subclasses.
   virtual void ReturnDefinition(Definition* definition) {
@@ -491,9 +496,6 @@
   virtual void ReturnDefinition(Definition* definition) {
     ReturnValue(Bind(definition));
   }
-
-  virtual void BuildTypeTest(ComparisonNode* node);
-  virtual void BuildTypeCast(ComparisonNode* node);
 };