Allows turning on checked mode on a per-isolate basis

runtime/vm/flow_graph_compiler.cc

Index: runtime/vm/flow_graph_compiler.cc
===================================================================
--- runtime/vm/flow_graph_compiler.cc	(revision 43472)
+++ runtime/vm/flow_graph_compiler.cc	(working copy)
@@ -904,7 +904,7 @@
 void FlowGraphCompiler::TryIntrinsify() {
   // Intrinsification skips arguments checks, therefore disable if in checked
   // mode.
-  if (FLAG_intrinsify && !FLAG_enable_type_checks) {
+  if (FLAG_intrinsify && !I->TypeChecksEnabled()) {
     if (parsed_function().function().kind() == RawFunction::kImplicitGetter) {
       // An implicit getter must have a specific AST structure.
       const SequenceNode& sequence_node = *parsed_function().node_sequence();