Implement convertToBlob() in OffscreenCanvas

third_party/WebKit/LayoutTests/virtual/threaded/fast/idleToBlob/OffscreenCanvas-convertToBlob-webgl-main-expected.html

Index: third_party/WebKit/LayoutTests/virtual/threaded/fast/idleToBlob/OffscreenCanvas-convertToBlob-webgl-main-expected.html
diff --git a/third_party/WebKit/LayoutTests/virtual/threaded/fast/idleToBlob/OffscreenCanvas-convertToBlob-webgl-main-expected.html b/third_party/WebKit/LayoutTests/virtual/threaded/fast/idleToBlob/OffscreenCanvas-convertToBlob-webgl-main-expected.html
new file mode 100644
index 0000000000000000000000000000000000000000..61c4f5c4b117d39c33c90763180822cb5107b218
--- /dev/null
+++ b/third_party/WebKit/LayoutTests/virtual/threaded/fast/idleToBlob/OffscreenCanvas-convertToBlob-webgl-main-expected.html
@@ -0,0 +1,26 @@
+<img id="png"/>
+<script>
+if (window.testRunner) {
+  testRunner.waitUntilDone();
+}
+
+var pngImage = document.getElementById('png');
+function imageLoaded() {
+  if (window.testRunner) {
+    window.testRunner.notifyDone();
+  }
+}
+pngImage.addEventListener('load', imageLoaded);
+
+var canvas = document.createElement("canvas");
+canvas.width = 50;
+canvas.height = 50;
+var gl = canvas.getContext('webgl');
+gl.clearColor(0, 1, 0, 1);
+gl.clear(gl.COLOR_BUFFER_BIT);
+
+canvas.toBlob(function(blob) {
+  pngImage.src = URL.createObjectURL(blob);
+});
+</script>
+