Add type inference for `this` expressions.

pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart

Index: pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
index e93df1060c0ed5d1e433a9a57c89514173149b2a..f798680ed311a8dbeb295b210e9113364233ca6d 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
@@ -212,6 +212,8 @@ abstract class TypeInferrerImpl extends TypeInferrer {
 
   final TypeInferenceListener listener;
 
+  final InterfaceType thisType;
+
   /// Context information for the current closure, or `null` if we are not
   /// inside a closure.
   ClosureContext closureContext;
@@ -222,8 +224,8 @@ abstract class TypeInferrerImpl extends TypeInferrer {
   /// Not used when performing local inference.
   bool isImmediatelyEvident = true;
 
-  TypeInferrerImpl(
-      TypeInferenceEngineImpl engine, this.uri, this.listener, bool topLevel)
+  TypeInferrerImpl(TypeInferenceEngineImpl engine, this.uri, this.listener,
+      bool topLevel, this.thisType)
       : coreTypes = engine.coreTypes,
         strongMode = engine.strongMode,
         classHierarchy = engine.classHierarchy,