Fix http://dartbug.com/23578:

runtime/vm/intermediate_language_x64.cc

Index: runtime/vm/intermediate_language_x64.cc
diff --git a/runtime/vm/intermediate_language_x64.cc b/runtime/vm/intermediate_language_x64.cc
index 830df847bc4a9f25b94238128a8c2bcbe8c5f3dd..9474ebda0e8fa7deb5e71e3dd3e8a5122e5a75b3 100644
--- a/runtime/vm/intermediate_language_x64.cc
+++ b/runtime/vm/intermediate_language_x64.cc
@@ -23,7 +23,6 @@
 namespace dart {
 
 DECLARE_FLAG(bool, emit_edge_counters);
-DECLARE_FLAG(bool, enable_asserts);
 DECLARE_FLAG(int, optimization_counter_threshold);
 DECLARE_FLAG(bool, throw_on_javascript_int_overflow);
 DECLARE_FLAG(bool, use_osr);
@@ -330,13 +329,13 @@ static void EmitAssertBoolean(Register reg,
   ASSERT(locs->always_calls());
   Label done;
 
-  if (Isolate::Current()->TypeChecksEnabled()) {
+  if (Isolate::Current()->flags().type_checks()) {
     __ CompareObject(reg, Bool::True(), PP);
     __ j(EQUAL, &done, Assembler::kNearJump);
     __ CompareObject(reg, Bool::False(), PP);
     __ j(EQUAL, &done, Assembler::kNearJump);
   } else {
-    ASSERT(FLAG_enable_asserts);
+    ASSERT(Isolate::Current()->flags().asserts());
     __ CompareObject(reg, Object::null_instance(), PP);
     __ j(NOT_EQUAL, &done, Assembler::kNearJump);
   }