Fix unknown type error in html_*.dart

tools/dom/templates/html/dartium/html_dartium.darttemplate

 // 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.
 
 // DO NOT EDIT
 // Auto-generated dart:html library.
 
 /**
  * HTML elements and other resources for web-based applications that need to
  * interact with the browser and the DOM (Document Object Model).
@@ skipping 30 matching lines @@
 import 'dart:math';
 // TODO(vsm): Remove this when we can do the proper checking in
 // native code for custom elements.
 import 'dart:mirrors';
 import 'dart:nativewrappers';
 import 'dart:typed_data';
 import 'dart:web_gl' as gl;
 import 'dart:web_sql';
 // Not actually used, but imported since dart:html can generate these objects.
 import 'dart:svg' as svg;
+import 'dart:svg' show Matrix;
 import 'dart:web_audio' as web_audio;
 
 export 'dart:math' show Rectangle, Point;
 
 $!GENERATED_DART_FILES
 
 // Issue 14721, order important for WrappedEvent.
 part '$AUXILIARY_DIR/WrappedEvent.dart';
 part '$AUXILIARY_DIR/AttributeMap.dart';
 part '$AUXILIARY_DIR/CanvasImageSource.dart';
@@ skipping 49 matching lines @@
 /**
  * Root node for all content in a web page.
  */
 HtmlDocument get document {
   if (_document != null) {
     return _document;
   }
   _document = window.document;
   return _document;
 }