Implement type variables in mixin applications.

pkg/front_end/test/fasta/mixin.dart.outline.expect

 library;
 import self as self;
 import "dart:core" as core;
 
+class B extends self::Object&M1&M2 {
+  constructor •(dynamic value) → void
+    ;
+}
 abstract class M1 extends core::Object {
   constructor •() → void
     ;
   method m() → dynamic
     ;
 }
 abstract class M2 extends core::Object {
   constructor •() → void
     ;
   method m() → dynamic
     ;
 }
 class C extends self::Object&M1&M2 {
+  constructor •(dynamic value) → void
+    ;
+}
+abstract class G1<T extends core::Object> extends core::Object {
+  constructor •() → void
+    ;
+  method m() → dynamic
+    ;
+}
+class D<S extends core::Object> extends self::D^G1<self::D::S> {
   constructor •() → void
     ;
 }
 abstract class Object&M1 = core::Object with self::M1 {
 }
 abstract class Object&M1&M2 = self::Object&M1 with self::M2 {
 }
+abstract class Object&M1 = core::Object with self::M1 {
+}
+abstract class Object&M1&M2 = self::Object&M1 with self::M2 {
+}
+abstract class D^G1<S extends core::Object> = core::Object with self::G1<self::D^G1::S> {
+}
 static method main() → dynamic
   ;