Eliminate type checks that can successfully be performed at compile time.

runtime/vm/code_generator_x64.h

Index: runtime/vm/code_generator_x64.h
===================================================================
--- runtime/vm/code_generator_x64.h	(revision 6416)
+++ runtime/vm/code_generator_x64.h	(working copy)
@@ -164,10 +164,12 @@
 
   void GenerateInstanceOf(intptr_t node_id,
                           intptr_t token_index,
+                          AstNode* value,
                           const AbstractType& type,
                           bool negate_result);
   void GenerateAssertAssignable(intptr_t node_id,
                                 intptr_t token_index,
+                                AstNode* value,
                                 const AbstractType& dst_type,
                                 const String& dst_name);
   void GenerateArgumentTypeChecks();