Use prototype inheritance to reduce number of is check properties.

pkg/compiler/lib/src/js_emitter/type_test_generator.dart

Index: pkg/compiler/lib/src/js_emitter/type_test_generator.dart
diff --git a/pkg/compiler/lib/src/js_emitter/type_test_generator.dart b/pkg/compiler/lib/src/js_emitter/type_test_generator.dart
index 2c9ce0d9ee1c64dc6a725bbea143105464044714..a2db59dc22e2321da233987df97e6c8fe4639124 100644
--- a/pkg/compiler/lib/src/js_emitter/type_test_generator.dart
+++ b/pkg/compiler/lib/src/js_emitter/type_test_generator.dart
@@ -57,12 +57,16 @@ class TypeTestGenerator {
 
     TypeTestProperties result = new TypeTestProperties();
 
+    /// Generates an is-test if the test is not inherited from a superclass
+    /// anyway. This assumes that for every class an is-tests is generated

[floitsch, 2015/01/26 16:19:29]

-anyway-.

[herhut, 2015/01/27 11:37:20]

Done.

+    /// dyanically at runtime anyway. We also always generate tests against

[floitsch, 2015/01/26 16:19:29]

dynamically.

[herhut, 2015/01/27 11:37:19]

Done.

+    /// native classes.
+    /// TODO(herhut): Generate tests for native classes dynamically, as well.
     void generateIsTest(Element other) {
-      if (other == compiler.objectClass && other != classElement) {
-        // Avoid emitting `$isObject` on all classes but [Object].
-        return;
+      if (classElement.isNative ||
+          !compiler.world.isSubclassOf(classElement, other)) {
+        result.properties[namer.operatorIs(other)] = js('1');

[floitsch, 2015/01/26 16:19:29]

probably ok to have the 1 here instead of a function (since it would otherwise
blow up the code).

[herhut, 2015/01/27 11:37:20]

Acknowledged.

       }
-      result.properties[namer.operatorIs(other)] = js('true');
     }
 
     void generateFunctionTypeSignature(FunctionElement method,
@@ -108,8 +112,7 @@ class TypeTestGenerator {
 
     void generateTypeCheck(TypeCheck check) {
       ClassElement checkedClass = check.cls;
-      // We must not call [generateIsTest] since we also want is$Object.
-      result.properties[namer.operatorIs(checkedClass)] = js('true');
+      generateIsTest(checkedClass);
       Substitution substitution = check.substitution;
       if (substitution != null) {
         jsAst.Expression body = substitution.getCode(backend.rti);