Tweak toString() for better type inference

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 1504658fe41bef7fdcbd39ebce8ae41d496e153a..b195b1a1a40effea2e24d64785fa62e2f0d08256 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -20860,6 +20860,7 @@ class Location extends NativeFieldWrapperClass2 implements LocationBase {
   String toString() => _blink.BlinkLocation.instance.toString_Callback_0_(this);
 
 
+
 }
 // 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
@@ -23993,7 +23994,10 @@ class Node extends EventTarget {
   /**
    * Print out a String representation of this Node.
    */
-  String toString() => nodeValue == null ? super.toString() : nodeValue;
+  String toString() {
+    String value = nodeValue;  // Fetch DOM Node property once.
+    return value == null ? super.toString() : value;
+  }
   // To suppress missing implicit constructor warnings.
   factory Node._() { throw new UnsupportedError("Not supported"); }
 
@@ -31432,10 +31436,10 @@ class Url extends NativeFieldWrapperClass2 implements UrlUtils {
     if ((blob_OR_source_OR_stream is Blob || blob_OR_source_OR_stream == null)) {
       return _blink.BlinkURL.instance.createObjectURL_Callback_1_(blob_OR_source_OR_stream);
     }
-    if ((blob_OR_source_OR_stream is MediaStream)) {
+    if ((blob_OR_source_OR_stream is MediaSource)) {
       return _blink.BlinkURL.instance.createObjectURL_Callback_1_(blob_OR_source_OR_stream);
     }
-    if ((blob_OR_source_OR_stream is MediaSource)) {
+    if ((blob_OR_source_OR_stream is MediaStream)) {
       return _blink.BlinkURL.instance.createObjectURL_Callback_1_(blob_OR_source_OR_stream);
     }
     throw new ArgumentError("Incorrect number or type of arguments");