Allows turning on checked mode on a per-isolate basis

runtime/vm/intermediate_language.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/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/constant_propagator.h"
 #include "vm/cpu.h"
 #include "vm/dart_entry.h"
@@ skipping 1922 matching lines @@
       return value()->definition();
     }
     ConstantInstr* null_constant = flow_graph->constant_null();
     instantiator_type_arguments()->BindTo(null_constant);
   }
   return this;
 }
 
 
 Definition* InstantiateTypeArgumentsInstr::Canonicalize(FlowGraph* flow_graph) {
-  return (FLAG_enable_type_checks || HasUses()) ? this : NULL;
+  return (Isolate::Current()->TypeChecksEnabled() || HasUses()) ? this : NULL;
 }
 
 
 LocationSummary* DebugStepCheckInstr::MakeLocationSummary(Zone* zone,
                                                           bool opt) const {
   const intptr_t kNumInputs = 0;
   const intptr_t kNumTemps = 0;
   LocationSummary* locs = new(zone) LocationSummary(
       zone, kNumInputs, kNumTemps, LocationSummary::kCall);
   return locs;
@@ skipping 1536 matching lines @@
     case Token::kTRUNCDIV: return 0;
     case Token::kMOD: return 1;
     default: UNIMPLEMENTED(); return -1;
   }
 }
 
 
 #undef __
 
 }  // namespace dart