Implement override-based type inference for instance methods.

pkg/front_end/lib/src/fasta/kernel/kernel_class_builder.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.kernel_class_builder;
 
 import 'package:front_end/src/fasta/kernel/kernel_shadow_ast.dart'
     show KernelMember;
 
 import 'package:kernel/ast.dart'
@@ skipping 177 matching lines @@
   void checkOverride(
       Member declaredMember, Member interfaceMember, bool isSetter) {
     if (declaredMember is Constructor || interfaceMember is Constructor) {
       internalError(
           "Constructor in override check.", fileUri, declaredMember.fileOffset);
     }
     if (declaredMember is Procedure && interfaceMember is Procedure) {
       if (declaredMember.kind == ProcedureKind.Method &&
           interfaceMember.kind == ProcedureKind.Method) {
         checkMethodOverride(declaredMember, interfaceMember);
-        return;
       }
     }
     // TODO(ahe): Handle other cases: accessors, operators, and fields.
 
     // Also record any cases where a field or getter/setter overrides something
     // in a superclass, since this information will be needed for type
     // inference.
     if (declaredMember is KernelMember &&
         identical(declaredMember.enclosingClass, cls)) {
       KernelMember.recordOverride(declaredMember, interfaceMember);
@@ skipping 85 matching lines @@
       }
     }
   }
 
   String get fullNameForErrors {
     return isMixinApplication
         ? "${supertype.fullNameForErrors} with ${mixedInType.fullNameForErrors}"
         : name;
   }
 }