Allows turning on checked mode on a per-isolate basis

runtime/vm/intermediate_language_x64.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/dart_entry.h"
@@ skipping 314 matching lines @@
 static void EmitAssertBoolean(Register reg,
                               intptr_t token_pos,
                               intptr_t deopt_id,
                               LocationSummary* locs,
                               FlowGraphCompiler* compiler) {
   // Check that the type of the value is allowed in conditional context.
   // Call the runtime if the object is not bool::true or bool::false.
   ASSERT(locs->always_calls());
   Label done;
 
-  if (FLAG_enable_type_checks) {
+  if (Isolate::Current()->TypeChecksEnabled()) {
     __ 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);
     __ CompareObject(reg, Object::null_instance(), PP);
     __ j(NOT_EQUAL, &done, Assembler::kNearJump);
   }
 
@@ skipping 6096 matching lines @@
   __ Drop(1);
   __ popq(result);
 }
 
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64