Converting Polymer's WebComponentsLoaded to an onReady future

pkg/polymer/lib/src/loader.dart

Index: pkg/polymer/lib/src/loader.dart
diff --git a/pkg/polymer/lib/src/loader.dart b/pkg/polymer/lib/src/loader.dart
index 844b6264f645a52dc9003181a727d25b0d6876c5..28cbd1e711f7afa217eb9c8c30c16fc6d9514cd8 100644
--- a/pkg/polymer/lib/src/loader.dart
+++ b/pkg/polymer/lib/src/loader.dart
@@ -42,10 +42,11 @@ void initPolymer(List<String> libraries, [String srcUrl]) {
       _loadLibrary(lib, srcUrl);
     }
 
-    // TODO(jmesserly): this should be in the custom_element polyfill, not here.
-    // notify the system that we are bootstrapped
-    document.body.dispatchEvent(
-        new CustomEvent('WebComponentsReady', canBubble: true));
+    Polymer._ready.complete();
+
+    // TODO(sigmund): move to boot.dart once it's ready.
+    document.body.style.transition = 'opacity 0.3s';
+    document.body.style.opacity = '1';
   });
 }