Define ImageBitmapSource in terms of CanvasImageSource

Also remove erroneous mentions of CanvasRenderingContext2D as a
CanvasImageSource type. Further cleanup of #790.

See 740634d and
43ad288 for prior commits in this area.

Fixes #893.

source

@@ -59276,7 +59276,6 @@ callback <dfn>BlobCallback</dfn> = void (<span>Blob</span>? blob);</pre>
 typedef (<span>HTMLOrSVGImageElement</span> or
          <span>HTMLVideoElement</span> or
          <span>HTMLCanvasElement</span> or
-         <span>CanvasRenderingContext2D</span> or
          <span>ImageBitmap</span>) <dfn>CanvasImageSource</dfn>;
 
 enum <dfn>CanvasFillRule</dfn> { "<span data-x="dom-context-2d-fillRule-nonzero">nonzero</span>", "<span data-x="dom-context-2d-fillRule-evenodd">evenodd</span>" };
@@ -61847,8 +61846,6 @@ try {
 
    <li><code>HTMLCanvasElement</code> (<code>canvas</code> elements)</li>
 
-   <li><code>CanvasRenderingContext2D</code></li>
-
    <li><code>ImageBitmap</code></li>
 
   </ul>
@@ -61919,10 +61916,6 @@ try {
   <p>When a <code>CanvasImageSource</code> object represents an <code>HTMLCanvasElement</code>, the
   element's bitmap must be used as the source image.</p>
 
-  <p>When a <code>CanvasImageSource</code> object represents a
-  <code>CanvasRenderingContext2D</code>, the object's <span>output bitmap</span> must be used as
-  the source image.</p>
-
   <p>When a <code>CanvasImageSource</code> object represents an element that is <span>being
   rendered</span> and that element has been resized, the original image data of the source image
   must be used, not the image as it is rendered (e.g. <code data-x="attr-dim-width">width</code> and
@@ -61933,15 +61926,11 @@ try {
   <p>When a <code>CanvasImageSource</code> object represents an <code>ImageBitmap</code>, the
   object's bitmap image data must be used as the source image.</p>
 
-<!--ADD-TOPIC:Security-->
   <p><dfn>The <var>image argument</var> is not origin-clean</dfn> if it is an
   <code>HTMLOrSVGImageElement</code> or <code>HTMLVideoElement</code> whose <span>origin</span> is
   not the <span data-x="same origin">same</span> as the <span>origin</span> specified by the
   <span>entry settings object</span>, or if it is an <code>HTMLCanvasElement</code> whose bitmap's
-  <span data-x="concept-canvas-origin-clean">origin-clean</span> flag is false, or if it is a
-  <code>CanvasRenderingContext2D</code> object whose <span
-  data-x="concept-canvas-origin-clean">origin-clean</span> flag is false.</p>
-<!--REMOVE-TOPIC:Security-->
+  <span data-x="concept-canvas-origin-clean">origin-clean</span> flag is false.</p>
 
 
 
@@ -63294,10 +63283,9 @@ v6DVT (also check for '- -' bits in the part above) -->
     data-x="dom-context-2d-imageSmoothingEnabled">imageSmoothingEnabled</code> attribute is set to
     true.</p>
 
-    <p class="note">When a <code>canvas</code> or <code>CanvasRenderingContext2D</code> object is
-    drawn onto itself, the <span>drawing model</span> requires the source to be copied before the
-    image is drawn, so it is possible to copy parts of a <code>canvas</code> or <span>output
-    bitmap</span> onto overlapping parts of itself.</p>
+    <p class="note">When a <code>canvas</code> element is drawn onto itself, the <span>drawing
+    model</span> requires the source to be copied before the image is drawn, so it is possible to
+    copy parts of a <code>canvas</code> element onto overlapping parts of itself.</p>
 
     <p>If the original image data is a bitmap image, the value painted at a point in the destination
     rectangle is computed by filtering the original image data. The user agent may use any filtering
@@ -91277,12 +91265,9 @@ interface <dfn>ImageBitmap</dfn> {
   void <span data-x="dom-ImageBitmap-close">close</span>();
 };
 
-typedef (<span>HTMLOrSVGImageElement</span> or
-         <span>HTMLVideoElement</span> or
-         <span>HTMLCanvasElement</span> or
+typedef (<span>CanvasImageSource</span> or
          <span>Blob</span> or
-         <span>ImageData</span> or
-         <span>ImageBitmap</span>) <dfn>ImageBitmapSource</dfn>;
+         <span>ImageData</span>) <dfn>ImageBitmapSource</dfn>;
 
 enum <dfn>ImageOrientation</dfn> { "<span data-x="dom-ImageOrientation-none">none</span>", "<span data-x="dom-ImageOrientation-flipY">flipY</span>" };
 enum <dfn>PremultiplyAlpha</dfn> { "<span data-x="dom-PremultiplyAlpha-none">none</span>", "<span data-x="dom-PremultiplyAlpha-premultiply">premultiply</span>", "<span data-x="dom-PremultiplyAlpha-default">default</span>" };
@@ -91332,10 +91317,9 @@ dictionary <dfn>ImageBitmapOptions</dfn> {
 
     <p>Rejects the promise with an <span>"<code>InvalidStateError</code>"</span>
     <code>DOMException</code> if the source image is not in a valid state (e.g. an <code>img</code>
-    element that hasn't loaded successfully, or a <code>CanvasRenderingContext2D</code> object whose
-    bitmap data has zero length along one or both dimensions, an <code>ImageBitmap</code> object
-    whose [[<span>Detached</span>]] internal slot value is true, an <code>ImageData</code> object
-    whose <code data-x="dom-imagedata-data">data</code> attribute value's [[<span>Detached</span>]]
+    element that hasn't loaded successfully, an <code>ImageBitmap</code> object whose
+    [[<span>Detached</span>]] internal slot value is true, an <code>ImageData</code> object whose
+    <code data-x="dom-imagedata-data">data</code> attribute value's [[<span>Detached</span>]]
     internal slot value is true, or a <code>Blob</code> whose data cannot be interpreted as a bitmap
     image).</p>