Implement override-based type inference for instance methods.

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

Index: pkg/front_end/lib/src/fasta/type_inference/type_schema_environment.dart
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_schema_environment.dart b/pkg/front_end/lib/src/fasta/type_inference/type_schema_environment.dart
index 4336d919eaca55405599ca5ea3f1f6d53c9cc72e..40b8d06b447b869da141a74b6aa12f1267a59927 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_schema_environment.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_schema_environment.dart
@@ -13,6 +13,23 @@ import 'package:kernel/core_types.dart';
 import 'package:kernel/type_algebra.dart';
 import 'package:kernel/type_environment.dart';
 
+// TODO(paulberry): try to push this functionality into kernel.
+FunctionType substituteTypeParams(
+    FunctionType type,
+    Map<TypeParameter, DartType> substitutionMap,
+    List<TypeParameter> newTypeParameters) {
+  var substitution = Substitution.fromMap(substitutionMap);
+  return new FunctionType(
+      type.positionalParameters.map(substitution.substituteType).toList(),
+      substitution.substituteType(type.returnType),
+      namedParameters: type.namedParameters
+          .map((named) => new NamedType(
+              named.name, substitution.substituteType(named.type)))
+          .toList(),
+      typeParameters: newTypeParameters,

[Siggi Cherem (dart-lang), 2017/06/21 20:19:08]

Just making sure I follow the change here. Before you had substitutionMap.keys,
was that basically using the old type-parameters instead of the new ones?

[Paul Berry, 2017/06/21 20:54:47]

That's right.  It was a bug which happened to be benign, because prior to this
CL, the only caller of this function didn't actually depend on the type
parameters being correct.  But now that I'm using this function to actually set
an inferred type, it actually matters that the type parameters are correct :)

+      requiredParameterCount: type.requiredParameterCount);
+}
+
 /// A constraint on a type parameter that we're inferring.
 class TypeConstraint {
   /// The lower bound of the type being constrained.  This bound must be a