Make getLineDash return [] instead of null if it has not yet been set.

tools/dom/templates/html/impl/impl_CanvasRenderingContext2D.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.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 $!MEMBERS
 
   /**
@@ skipping 243 matching lines @@
 
 $if DART2JS
   @DomName('CanvasRenderingContext2D.lineDashOffset')
   num get lineDashOffset => JS('num',
       '#.lineDashOffset || #.webkitLineDashOffset', this, this);
 
   @DomName('CanvasRenderingContext2D.lineDashOffset')
   void set lineDashOffset(num value) => JS('void',
       'typeof #.lineDashOffset != "undefined" ? #.lineDashOffset = # : '
       '#.webkitLineDashOffset = #', this, this, value, this, value);
+
+  @DomName('CanvasRenderingContext2D.getLineDash')
+  List<num> getLineDash() => _getLineDash();
 $else
+  @DomName('CanvasRenderingContext2D.getLineDash')
+  List<num> getLineDash() {
+    var result = _getLineDash();
+    if (result == null) {
+      result = [];
+    }
+    return result;
+  }
   // TODO(amouravski): Add Dartium native methods for drawImage once we figure
   // out how to not break native bindings.
 $endif
 $if DART2JS
 
   /**
    * Draws text to the canvas.
    *
    * The text is drawn starting at coordinates ([x], [y]).
    * If [maxWidth] is provided and the [text] is computed to be wider than
@@ skipping 10 matching lines @@
   void fillText(String text, num x, num y, [num maxWidth]) {
     if (maxWidth != null) {
       JS('void', '#.fillText(#, #, #, #)', this, text, x, y, maxWidth);
     } else {
       JS('void', '#.fillText(#, #, #)', this, text, x, y);
     }
   }
 $endif
 }