Update pixel test expectation and add new worker tests

third_party/WebKit/LayoutTests/fast/canvas/OffscreenCanvas-commit-main.html

-<!DOCTYPE>
-<canvas id="canvas2D" width="50" height="50" background-color="red"></canvas>
-<script>
-// Note: If someone see this test flaky in the future, please mark the test as
-// flaky; the code itself is not the cause of such flakiness.
-// TODO(xlai): Guarantee all OffscreenCanvas commit tests non-flaky under all cases.
-// See crbug.com/645173.
-
-// Currently, we push a Green color frame from OffscreenCanvas; so we test
-// whether the associated canvas has green pixel. In the future, when we
-// change solidColorFrame to textureFrame, the expected png needs to changed too.
-var canvas2D = document.getElementById("canvas2D");
-var offscreenCanvas = canvas2D.transferControlToOffscreen();
-var offscreen2d = offscreenCanvas.getContext("2d");
-offscreen2d.commit();
-</script>