fast-startup: do not emit inherit calls for classes from different fragments

pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart

Index: pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart b/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
index 69e3deaa21a3b486efac3a8551506f72e54028b8..3e1127847a59d29fe78f0bd8f7f61786925ac1f9 100644
--- a/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/startup_emitter/fragment_emitter.dart
@@ -794,13 +794,20 @@ class FragmentEmitter {
     List<js.Expression> inheritCalls = <js.Expression>[];
     List<js.Expression> mixinCalls = <js.Expression>[];
 
+    Set<Class> classesInFragment = new Set<Class>();
+    for (Library library in fragment.libraries) {
+      classesInFragment.addAll(library.classes);
+    }
+
     Set<Class> emittedClasses = new Set<Class>();
 
     void emitInheritanceForClass(cls) {
       if (cls == null || emittedClasses.contains(cls)) return;
 
       Class superclass = cls.superclass;
-      emitInheritanceForClass(superclass);
+      if (classesInFragment.contains(superclass)) {
+        emitInheritanceForClass(superclass);
+      }
 
       js.Expression superclassReference = (superclass == null)
           ? new js.LiteralNull()