sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index c2181cfb6c584f3a60747f19202edb67eec722b1..ae704df9a27d9ae2bea76a84c660a95139e785d0 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -27872,7 +27872,7 @@ class Window extends EventTarget implements WindowBase {
    * frame unwinds, causing the future to complete after all processing has
    * completed for the current event, but before any subsequent events.
    */
-  void setImmediate(TimeoutHandler callback) { 
+  void setImmediate(TimeoutHandler callback) {
     _addMicrotaskCallback(callback);
   }
   /**
@@ -27880,8 +27880,11 @@ class Window extends EventTarget implements WindowBase {
    * registered under [name].
    */
   SendPortSync lookupPort(String name) {
-    var port =
-        json.parse(document.documentElement.attributes['dart-port:$name']);
+    var portStr = document.documentElement.attributes['dart-port:$name'];
+    if (portStr == null) {
+      return null;
+    }
+    var port = json.parse(portStr);
     return _deserialize(port);
   }
 
@@ -27903,7 +27906,7 @@ class Window extends EventTarget implements WindowBase {
    * If you need to later cancel this animation, use [requestAnimationFrame]
    * instead.
    *
-   * Note: The code that runs when the future completes should call 
+   * Note: The code that runs when the future completes should call
    * [animationFrame] again for the animation to continue.
    */
   Future<num> get animationFrame {