Reland and fix bug: Don't store redundant compile-type at values.

runtime/vm/flow_graph_type_propagator.cc

Index: runtime/vm/flow_graph_type_propagator.cc
===================================================================
--- runtime/vm/flow_graph_type_propagator.cc	(revision 41847)
+++ runtime/vm/flow_graph_type_propagator.cc	(working copy)
@@ -241,6 +241,11 @@
 
 void FlowGraphTypePropagator::VisitValue(Value* value) {
   CompileType* type = TypeOf(value->definition());
+  if (type == value->definition()->Type()) {
+    value->SetReachingType(NULL);
+    return;
+  }
+
   value->SetReachingType(type);
 
   if (FLAG_trace_type_propagation) {
@@ -641,7 +646,7 @@
 
 CompileType* Value::Type() {
   if (reaching_type_ == NULL) {
-    reaching_type_ = definition()->Type();
+    return definition()->Type();
   }
   return reaching_type_;
 }