Flatten inferrer implementation

pkg/compiler/lib/src/inferrer/node_tracer.dart

Index: pkg/compiler/lib/src/inferrer/node_tracer.dart
diff --git a/pkg/compiler/lib/src/inferrer/node_tracer.dart b/pkg/compiler/lib/src/inferrer/node_tracer.dart
index 72c696544da8b226e23a4ab927b424aa5731a951..52617803529eece3a87de9d89771e17b9711e87a 100644
--- a/pkg/compiler/lib/src/inferrer/node_tracer.dart
+++ b/pkg/compiler/lib/src/inferrer/node_tracer.dart
@@ -10,7 +10,7 @@ import '../elements/elements.dart';
 import '../types/types.dart' show ContainerTypeMask, MapTypeMask;
 import '../util/util.dart' show Setlet;
 import 'debug.dart' as debug;
-import 'type_graph_inferrer.dart' show TypeGraphInferrerEngine;
+import 'inferrer_engine.dart';
 import 'type_graph_nodes.dart';
 
 // A set of selectors we know do not escape the elements inside the
@@ -72,16 +72,15 @@ Set<String> doesNotEscapeMapSet = new Set<String>.from(const <String>[
 ]);
 
 /// Common logic to trace a value through the type inference graph nodes.
-abstract class TracerVisitor<T extends TypeInformation>
-    implements TypeInformationVisitor {
-  final T tracedType;
-  final TypeGraphInferrerEngine inferrer;
+abstract class TracerVisitor implements TypeInformationVisitor {
+  final TypeInformation tracedType;
+  final InferrerEngine inferrer;
   final Compiler compiler;
 
   static const int MAX_ANALYSIS_COUNT = 16;
   final Setlet<Element> analyzedElements = new Setlet<Element>();
 
-  TracerVisitor(this.tracedType, TypeGraphInferrerEngine inferrer)
+  TracerVisitor(this.tracedType, InferrerEngine inferrer)
       : this.inferrer = inferrer,
         this.compiler = inferrer.compiler;