Tightening up dart2js load timing.

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

Index: sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart b/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
index 2302aec5576d8b4dd92cbe738a3cf234332b6724..b98d5a25fa27ddcfc6b4db8856d68b567026a8ec 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart
@@ -857,11 +857,7 @@ class CodeEmitterTask extends CompilerTask {
     return js.fun('oldIsolate', [
       js('var isolateProperties = oldIsolate.${namer.isolatePropertiesName}'),
 
-      js(r'isolateProperties.$currentScript ='
-              'typeof document == "object" ?'
-              '(document.currentScript ||'
-                     'document.scripts[document.scripts.length - 1]) :'
-              'null'),
+      js(r'isolateProperties.$currentScript = null'),
 
       js('var isolatePrototype = oldIsolate.prototype'),
       js('var str = "{\\n"'),
@@ -2942,23 +2938,42 @@ class CodeEmitterTask extends CompilerTask {
     }
     addComment('BEGIN invoke [main].', buffer);
     buffer.write("""
-if (typeof document !== "undefined" && document.readyState !== "complete") {
-  document.addEventListener("readystatechange", function () {
-    if (document.readyState == "complete") {
-      if (typeof dartMainRunner === "function") {
-        dartMainRunner(function() { ${mainCall}; });
-      } else {
-        ${mainCall};
-      }
+(function (callback) {
+  if (!self.document) {

[ahe, 2013/08/07 16:24:47]

Just a quick note, sorry.

This will break dart2js tests running on d8.  This is what we test on the main
build bots.

Try running:

./tools/test.py -mrelease -cdart2js -rd8

[blois, 2013/08/07 17:39:50]

Ah, thanks!

+    callback(null);
+    return;
+  }
+  if (document.currentScript) {
+    callback(document.currentScript);
+    return;
+  }
+
+  var scripts = document.scripts;
+  function onLoad() {
+    for (var i = 0; i < scripts.length; ++i) {
+      scripts[i].removeEventListener('load', onLoad, false);

[vsm, 2013/08/07 16:10:12]

Can you add a comment here to explain what's going on?  If you hadn't explained
it ahead of time, I think I'd be pretty befuddled here.  Even still, it's tricky
code.

[blois, 2013/08/07 17:39:50]

Done.

     }
-  }, false);
-} else {
+    callback(event.target);
+  }
+  for (var i = 0; i < scripts.length; ++i) {
+    scripts[i].addEventListener('load', onLoad, false);
+  }
+})(function(currentScript) {
+  Isolate.\$isolateProperties.\$currentScript = currentScript;
+
+  if (self.console && self.document && document.readyState == "loading") {
+    // Bug dartbug.com/12281 this warning is to let users know how to match
+    // Dartium execution timing.
+    console.warn("Dart script executed synchronously, use <script src='" +
+        currentScript.src + "' defer></scr" + "ipt> to execute after parsing " +
+        "has completed.");
+  }
   if (typeof dartMainRunner === "function") {
     dartMainRunner(function() { ${mainCall}; });
   } else {
     ${mainCall};
   }
-}
+});
 """);
     addComment('END invoke [main].', buffer);
   }