Updates on canvas backreference for canvas rendering contexts

third_party/WebKit/LayoutTests/fast/canvas/rendering-contexts-back-references.html

+<script src="../../resources/testharness.js"></script>
+<script src="../../resources/testharnessreport.js"></script>
+<script>
+function generateTest(canvas, context, anotherCanvas, message)

[Justin Novosad, 2016/08/10 18:56:33]

I meant use "generate_tests" from testharness.js instead of using "test" below.

[xlai (Olivia), 2016/08/10 20:51:29]

Done.

+{
+    assert_equals(context.canvas, canvas);
+    context.canvas = anotherCanvas;
+    assert_not_equals(context.canvas, anotherCanvas, message);
+}
+
+// Back reference to html canvas
+test(function() {
+    var htmlCanvas = document.createElement("canvas");
+    generateTest(htmlCanvas, htmlCanvas.getContext("2d"), document.createElement("canvas"), "ctx2d.canvas is read-only."); 
+}, "Test back references to html canvas for CanvasRenderingContext2D");
+
+test(function() {
+    var htmlCanvas = document.createElement("canvas");
+    generateTest(htmlCanvas, htmlCanvas.getContext("webgl"), document.createElement("canvas"), "webglCtx.canvas is read-only."); 
+}, "back references to html canvas for WebglRenderingContext");
+
+test(function() {
+    var htmlCanvas = document.createElement("canvas");
+    generateTest(htmlCanvas, htmlCanvas.getContext("bitmaprenderer"), document.createElement("canvas"), "bitmaprenderer.canvas is read-only.");
+}, "back references to canvas for ImageBitmapRenderingContext");
+
+// Back reference to Offscreen canvas
+test(function() {
+    var offscreenCanvas = new OffscreenCanvas(10, 10);
+    generateTest(offscreenCanvas, offscreenCanvas.getContext("2d"), new OffscreenCanvas(10, 10), "ctx2d.canvas is read-only.");
+}, "back references to offscreencanvas for OffscreenCanvasRenderingContext2D");
+
+test(function() {
+    var offscreenCanvas = new OffscreenCanvas(10, 10);
+    generateTest(offscreenCanvas, offscreenCanvas.getContext("webgl"), new OffscreenCanvas(10, 10), "webgl.canvas is read-only.");
+}, "back references to offscreencanvas for WebglRenderingContext");
+
+</script>