Sync HTML element interfaces C-D with the spec

Source/core/html/HTMLCanvasElement.idl

 /*
  * Copyright (C) 2006, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. 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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 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.
  */
 
+// https://html.spec.whatwg.org/#htmlcanvaselement
+
 typedef (CanvasRenderingContext2D or WebGLRenderingContext) RenderingContext;
 
 interface HTMLCanvasElement : HTMLElement {
-
+    // FIXME: width and height should be unsigned long.
     attribute long width;
     attribute long height;
 
-    [RaisesException] DOMString toDataURL(optional DOMString? type = null, optional any arguments);
-
     // Note: this differs deliberately from the specified Web IDL for this function:
     //     RenderingContext? getContext(DOMString contextId, any... arguments);
     // in order to eliminate the custom binding. It is functionally equivalent.
     //
     // The PermissiveDictionaryConversion extended attribute is needed to allow the
     // autogenerated code to match the behavior of the custom binding. Web IDL
     // requires throwing TypeError if the incoming argument is not an object type
     // (and is not undefined or null). The binding must ignore this.
     //
     // Also note: the only reason this must return type "any" is to allow the
     // InspectorInstrumentation wrappers to be called for canvases. If that could be
     // handled differently the return type could be changed to "RenderingContext?"
     // and the [CallWith=ScriptState] extended attribute removed.
+    //
+    // FIXME: The contextId argument should not be optional.
     [CallWith=ScriptState] any getContext([Default=Undefined] optional DOMString contextId, [PermissiveDictionaryConversion] optional CanvasContextCreationAttributes attributes);
+
+    // Note: The arguments argument is variadic in the spec, but not here as
+    // only one extra argument is actually used.
+    // FIXME: type should not be nullable or have a default value.
+    [RaisesException] DOMString toDataURL(optional DOMString? type = null, optional any arguments);
 };