Added docs to canvaselement. Giving it docs for all members.

tools/dom/templates/html/impl/impl_HTMLCanvasElement.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 CanvasImageSource$IMPLEMENTS$NATIVESPEC {
 $!MEMBERS
   /** An API for drawing on this canvas. */
 $if DART2JS
   CanvasRenderingContext2D get context2D =>
       JS('Null|CanvasRenderingContext2D', '#.getContext(#)', this, '2d');
 $else
   CanvasRenderingContext2D get context2D => getContext('2d');
 $endif
 
+  /**
+   * Returns a new Web GL context for this canvas.
+   *
+   * ## Other resources
+   *
+   * * [WebGL fundamentals]
+   * (http://www.html5rocks.com/en/tutorials/webgl/webgl_fundamentals/) from
+   * HTML5Rocks.
+   * * [WebGL homepage] (http://get.webgl.org/).
+   */
   @SupportedBrowser(SupportedBrowser.CHROME)
   @SupportedBrowser(SupportedBrowser.FIREFOX)
   @Experimental()
   gl.RenderingContext getContext3d({alpha: true, depth: true, stencil: false,
     antialias: true, premultipliedAlpha: true, preserveDrawingBuffer: false}) {
 
     var options = {
       'alpha': alpha,
       'depth': depth,
       'stencil': stencil,
@@ skipping 45 matching lines @@
    *
    * * [Data URI Scheme](http://en.wikipedia.org/wiki/Data_URI_scheme) from Wikipedia.
    *
    * * [HTMLCanvasElement](https://developer.mozilla.org/en-US/docs/DOM/HTMLCanvasElement) from MDN.
    *
    * * [toDataUrl](http://dev.w3.org/html5/spec/the-canvas-element.html#dom-canvas-todataurl) from W3C.
    */
   String toDataUrl([String type = 'image/png', num quality]) =>
       _toDataUrl(type, quality);
 }