Control static type propagation with a flag in optimizing compiler.

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
===================================================================
--- runtime/vm/compiler.cc	(revision 12600)
+++ runtime/vm/compiler.cc	(working copy)
@@ -39,6 +39,7 @@
     "Do conditional constant propagation/unreachable code elimination.");
 DEFINE_FLAG(bool, cse, true, "Do common subexpression elimination.");
 DEFINE_FLAG(bool, licm, true, "Do loop invariant code motion.");
+DEFINE_FLAG(bool, propagate_types, true, "Do static type propagation.");
 DEFINE_FLAG(int, deoptimization_counter_threshold, 5,
     "How many times we allow deoptimization before we disallow"
     " certain optimizations");
@@ -181,8 +182,10 @@
         }
 
         // Propagate types and eliminate more type tests.
-        FlowGraphTypePropagator propagator(flow_graph);
-        propagator.PropagateTypes();
+        if (FLAG_propagate_types) {
+          FlowGraphTypePropagator propagator(flow_graph);
+          propagator.PropagateTypes();
+        }
 
         // Verify that the use lists are still valid.
         DEBUG_ASSERT(flow_graph->ValidateUseLists());