Revert "Element.style is not null"

Need to investigate:
FAILED: dart2js-chrome release_ia32 co19/LayoutTests/fast/xsl/default-html_t01
Expected: RuntimeError
Actual: Pass

Review URL: https://codereview.chromium.org//971033004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@44222 260f80e4-7a28-3924-810f-c04153c831b5

sdk/lib/html/dart2js/html_dart2js.dart

@@ -12667,7 +12667,6 @@ abstract class Element extends Node implements GlobalEventHandlers, ParentNode,
 
   @DomName('Element.style')
   @DocsEditable()
-  @Returns('CssStyleDeclaration')
   final CssStyleDeclaration style;
 
   @DomName('Element.tagName')

tools/dom/scripts/dartmetadata.py

@@ -108,10 +108,6 @@ _dart2js_annotations = monitored.Dict('dartmetadata._dart2js_annotations', {
       "@Returns('NodeList|HtmlCollection')",
     ],
 
-    'Element.style': [  # Element.style is never null.
-      "@Returns('CssStyleDeclaration')",
-    ],
-
     "ErrorEvent.error": [
       "@Creates('Null')", # Only returns values created elsewhere.
     ],