Dont install methods if implementation superclass corresponds to an installed extension class

tool/input_sdk/private/ddc_runtime/classes.dart

Index: tool/input_sdk/private/ddc_runtime/classes.dart
diff --git a/tool/input_sdk/private/ddc_runtime/classes.dart b/tool/input_sdk/private/ddc_runtime/classes.dart
index dab53e77298e7a9dbdc2dd96c2771ba431ba78f8..95faf3deb3a1c558e3056c7b481178c95f5ac995 100644
--- a/tool/input_sdk/private/ddc_runtime/classes.dart
+++ b/tool/input_sdk/private/ddc_runtime/classes.dart
@@ -279,10 +279,30 @@ getExtensionSymbol(name) {
 defineExtensionNames(names) =>
     JS('', '#.forEach(#)', names, getExtensionSymbol);
 
+
+int _t1 = 0, _t2 = 0;
+void tick1() {
+  _t1 = JS('int', '# + 1', _t1);
+  if (JS('bool', '# % 100 == 0', _t1)) JS('', 'console.log([#, #])', _t1, _t2);
+}
+void tick2() {
+  _t2 = JS('int', '# + 1', _t2);
+  if (JS('bool', '# % 100 == 0', _t2)) JS('', 'console.log([#, #])', _t1, _t2);
+}
+
 // Install properties in prototype order.  Properties / descriptors from
 // more specific types should overwrite ones from less specific types.
 _installProperties(jsProto, extProto) {
+  tick1();
   var coreObjProto = JS('', '#.prototype', Object);
+  _installProperties2(jsProto, extProto, coreObjProto);
+  // Mark this jsProto as being the prototype for the extension class.
+  // TODO(sra): Fix the tagging.
+  JS('', '#._xxx = #', jsProto, extProto);
+}
+
+_installProperties2(jsProto, extProto, coreObjProto) {
+  tick2();
   if (JS('bool', '# === #', extProto, coreObjProto)) {
      // core.Object members need to be copied from the non-symbol name to the
      // symbol name.
@@ -295,7 +315,12 @@ _installProperties(jsProto, extProto) {
     return;
   }
   if (JS('bool', '# !== #', jsProto, extProto)) {
-    _installProperties(jsProto, JS('', '#.__proto__', extProto));
+    var extParent = JS('', '#.__proto__', extProto);
+    // If the js parent is the extension class parent, we inherit all the
+    // extension class methods via prototype inheritance.
+    if(JS('bool', '#.__proto__._xxx !== #', jsProto, extParent)) {

[Leaf, 2016/05/16 18:03:07]

Maybe use a symbol to be more robust?  Or maybe just a better obfuscated name
(e.g. __ddc_extension_prototype or something)?

+      _installProperties2(jsProto, extParent, coreObjProto);
+    }
   }
   copyTheseProperties(jsProto, extProto, getOwnPropertySymbols(extProto));
 }