Removing dart2js main execution warning message

sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 2998 matching lines @@
       scripts[i].removeEventListener("load", onLoad, false);
     }
     callback(event.target);
   }
   for (var i = 0; i < scripts.length; ++i) {
     scripts[i].addEventListener("load", onLoad, false);
   }
 })(function(currentScript) {
   init.currentScript = currentScript;
 
-  if (typeof console !== "undefined" && typeof document !== "undefined" &&
-      document.readyState == "loading") {
-    console.warn("Dart script executed synchronously, use <script src='" +
-        currentScript.src + "' defer></scr" + "ipt> to execute after parsing " +
-        "has completed. See also http://dartbug.com/12281.");
-  }
   if (typeof dartMainRunner === "function") {
     dartMainRunner(function() { ${mainCall}; });
   } else {
     ${mainCall};
   }
 })$N''');
     addComment('END invoke [main].', buffer);
   }
 
   void emitGetInterceptorMethod(CodeBuffer buffer,
@@ skipping 1166 matching lines @@
 
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;