Implementing promise-based commit for driving OffscreenCanvas animations

content/test/data/gpu/pixel_offscreenCanvas_webgl_commit_worker.html

Index: content/test/data/gpu/pixel_offscreenCanvas_webgl_commit_worker.html
diff --git a/content/test/data/gpu/pixel_offscreenCanvas_webgl_commit_worker.html b/content/test/data/gpu/pixel_offscreenCanvas_webgl_commit_worker.html
index 292500ea9b39392e52a27e2ab9aa960d5fb866c0..1dfa64189dfcd568fd4e1f6fc5104e10b1498b85 100644
--- a/content/test/data/gpu/pixel_offscreenCanvas_webgl_commit_worker.html
+++ b/content/test/data/gpu/pixel_offscreenCanvas_webgl_commit_worker.html
@@ -15,9 +15,12 @@ that the baseline images are regenerated on the next run.
 }
 </style>
 <script id="myWorker" type="text/worker">
-function drawTriangle(canvas)
+
+var g_frameNumber = 0;
+var gl;
+
+function drawTriangle()
 {
-  var gl = canvas.getContext("webgl");
   gl.clearColor(0, 1, 0, 1);
   gl.clear(gl.COLOR_BUFFER_BIT);
 
@@ -60,10 +63,29 @@ function drawTriangle(canvas)
   gl.commit();
 }
 
+function drawLoop()
+{
+  if (g_frameNumber < 3) {
+    gl.clearColor(1, 0, 0, 1);
+    gl.clear(gl.COLOR_BUFFER_BIT);
+    g_frameNumber++;
+    gl.commit().then(drawLoop);
+  } else {
+    drawTriangle(offscreenCanvas);
+    gl.commit();
+
+    // The following clear is never committed
+    gl.clearColor(0, 0, 1, 1);
+    gl.clear(gl.COLOR_BUFFER_BIT);
+
+    self.postMessage("");
+  }
+}
+
 self.onmessage = function(e) {
   var transferredOffscreenCanvas = e.data;
-  drawTriangle(transferredOffscreenCanvas);
-  self.postMessage("");
+  gl = transferredOffscreenCanvas.getContext("webgl");
+  drawLoop();
 };
 </script>
 <script>