Update dart2js to fix #80.

test/kernel/regression/issue_000080.dart.txt

+library;
+import self as self;
+import "dart:core" as core;
+
+class Mixin extends core::Object {
+  field dynamic field;
+  constructor •() → self::Mixin
+    : super core::Object::•();
+  method foo() → dynamic
+    return 87;
+}
+class Foo extends self::Object+Mixin#0 {
+  constructor •() → self::Foo
+    : super self::Object+Mixin#0::•();
+  method foo() → dynamic
+    return super.self::Object+Mixin#0::foo();
+  method bar() → dynamic
+    return super.self::Object+Mixin#0::field;
+}
+abstract class Object+Mixin#0 extends core::Object implements self::Mixin {
+  field dynamic field;
+  constructor •() → dynamic
+    : super core::Object::•();
+  method foo() → dynamic
+    return 87;
+}
+static method main() → dynamic {
+  dynamic f = new self::Foo::•();
+  f.field = 42;
+  core::print(f.bar());
+}