Notify listeners on bitmaprenderer context changes

content/test/data/media/canvas_capture.html

Index: content/test/data/media/canvas_capture.html
diff --git a/content/test/data/media/canvas_capture.html b/content/test/data/media/canvas_capture.html
index 15a904264cd67b56b580adbe8d4a03ca7311dda7..1490c3da35b18ec4478ceadfe134084e66c7047d 100644
--- a/content/test/data/media/canvas_capture.html
+++ b/content/test/data/media/canvas_capture.html
@@ -33,6 +33,16 @@ function drawWebGL(canvas, drawCounter) {
   checkForRedraw(canvas, drawCounter, drawWebGL);
 };
 
+function drawBitmapRenderer(canvas, drawCounter) {
+  var gl = canvas.getContext('bitmaprenderer');
+  var offscreen = new OffscreenCanvas(400,200);
+  var ctx = offscreen.getContext('2d');
+  ctx.fillStyle = 'green';
+  ctx.fillRect(0, 0, canvas.width, canvas.height);
+  gl.transferFromImageBitmap(offscreen.transferToImageBitmap());
+  checkForRedraw(canvas, drawCounter, drawBitmapRenderer);
+};
+
 function testCanvasCapture(drawFunction) {
   var canvas = document.createElement('canvas');
   document.body.appendChild(canvas);