Convert keys in dataSet to camelCase instead of dasherized.

tools/dom/src/AttributeMap.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 html;
 
 abstract class _AttributeMap implements Map<String, String> {
   final Element _element;
 
   _AttributeMap(this._element);
@@ skipping 206 matching lines @@
   }
 
   int get length => keys.length;
 
   // TODO: Use lazy iterator when it is available on Map.
   bool get isEmpty => length == 0;
 
   bool get isNotEmpty => !isEmpty;
 
   // Helpers.
-  String _attr(String key) => 'data-$key';
+  String _attr(String key) => 'data-${_toHyphenedName(key)}';
   bool _matches(String key) => key.startsWith('data-');
-  String _strip(String key) => key.substring(5);
+  String _strip(String key) => _toCamelCase(key.substring(5));
+
+  /**
+   * Converts a string name with hyphens into an identifier, by removing hyphens
+   * and capitalizing the following letter. Optionally [startUppercase] to
+   * captialize the first letter.
+   */
+  String _toCamelCase(String hyphenedName, {bool startUppercase: false}) {
+    var segments = hyphenedName.split('-');
+    int start = startUppercase ? 0 : 1;
+    for (int i = start; i < segments.length; i++) {
+      var segment = segments[i];
+      if (segment.length > 0) {
+        // Character between 'a'..'z' mapped to 'A'..'Z'
+        segments[i] = '${segment[0].toUpperCase()}${segment.substring(1)}';
+      }
+    }
+    return segments.join('');
+  }
+
+  /** Reverse of [toCamelCase]. */
+  String _toHyphenedName(String word) {
+    var sb = new StringBuffer();
+    for (int i = 0; i < word.length; i++) {
+      var lower = word[i].toLowerCase();
+      if (word[i] != lower && i > 0) sb.write('-');
+      sb.write(lower);
+    }
+    return sb.toString();
+  }
 }