Fix all dartanalyzer errors in dart:sky except the Native ones.

sky/engine/core/html/canvas/Path2D.idl

 /*
  * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
  * Copyright (C) 2012, 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 12 matching lines @@
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
  * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
  * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 // http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#path2d
 
 [
     Constructor,
-    Constructor(Path2D path),
 ] interface Path2D {
     // FIXME(sky): Fix this object.
 };
 
 Path2D implements CanvasPathMethods;