Allows turning on checked mode on a per-isolate basis

runtime/vm/code_generator.cc

Index: runtime/vm/code_generator.cc
===================================================================
--- runtime/vm/code_generator.cc	(revision 43426)
+++ runtime/vm/code_generator.cc	(working copy)
@@ -227,7 +227,7 @@
   // Code inlined in the caller should have optimized the case where the
   // instantiator can be reused as type argument vector.
   ASSERT(instantiator.IsNull() || !type_arguments.IsUninstantiatedIdentity());
-  if (FLAG_enable_type_checks) {
+  if (FLAG_enable_type_checks || Isolate::Current()->checked_mode()) {
     Error& bound_error = Error::Handle();
     type_arguments =
         type_arguments.InstantiateAndCanonicalizeFrom(instantiator,
@@ -532,7 +532,7 @@
     }
     String& bound_error_message =  String::Handle();
     if (!bound_error.IsNull()) {
-      ASSERT(FLAG_enable_type_checks);
+      ASSERT(FLAG_enable_type_checks || Isolate::Current()->checked_mode());
       bound_error_message = String::New(bound_error.ToErrorCString());
     }
     if (src_type_name.Equals(dst_type_name)) {