Implement inferGenericFunctionOrType in front_end.

pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_test.dart

Index: pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_test.dart
diff --git a/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_test.dart b/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_test.dart
index 97d2a863ce9ce1698370904df7ddb0e505f43f3a..0d812a1b683ae3ae2514ce9bcc153c6251aaefc1 100644
--- a/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_test.dart
+++ b/pkg/front_end/test/fasta/type_inference/type_constraint_gatherer_test.dart
@@ -128,8 +128,11 @@ class TypeConstraintGathererTest {
       DartType a, DartType b, List<String> expectedConstraints) {
     var typeSchemaEnvironment =
         new TypeSchemaEnvironment(coreTypes, new ClassHierarchy(program));
-    var constraints =
-        subtypeMatch(typeSchemaEnvironment, [T1.parameter, T2.parameter], a, b);
+    var typeConstraintGatherer = new TypeConstraintGatherer(
+        typeSchemaEnvironment, [T1.parameter, T2.parameter]);
+    var constraints = typeConstraintGatherer.trySubtypeMatch(a, b)
+        ? typeConstraintGatherer.computeConstraints()
+        : null;
     if (expectedConstraints == null) {
       expect(constraints, isNull);
       return;