Fix image-decoder-to-texture in WebGL 2 mode. (KhronosGroup#3652)

The test was fetching nonexistent "width" and "height" properties on
the VideoFrame, leading to a (0, 0)-sized texture upload. codedWidth
and codedHeight are the best approximation without handling the full
visibleRect in the test.

Follow-on to KhronosGroup#3641 .

Associated with Chromium bug crbug.com/337904214 .

sdk/tests/conformance/textures/misc/image-decoder-to-texture.html

@@ -59,7 +59,7 @@
     }
     let frame = decodeResult.image;
     if (window.WebGL2RenderingContext && gl instanceof window.WebGL2RenderingContext) {
-        gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, frame.width, frame.height, 0, gl.RGBA, gl.UNSIGNED_BYTE, frame);
+        gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, frame.codedWidth, frame.codedHeight, 0, gl.RGBA, gl.UNSIGNED_BYTE, frame);
     } else {
         gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, frame);
     }