Add basic threaded compositor test to gpu_feature_browsertest.cc

chrome/test/data/gpu/feature_compositing.html

Index: chrome/test/data/gpu/feature_compositing.html
diff --git a/chrome/test/data/gpu/feature_compositing.html b/chrome/test/data/gpu/feature_compositing.html
index e834b8c536374a2d4fa2ae77e120e8dde62ba0d0..3f4f8811a5c8ca545dd3549e5bc16af05b9299c2 100644
--- a/chrome/test/data/gpu/feature_compositing.html
+++ b/chrome/test/data/gpu/feature_compositing.html
@@ -10,6 +10,8 @@ body {
 </style>
 <script>
 var frameCount = 0;
+// 3 is not enough for threaded compositing, using 6 to avoid racing.
+var totalRafs = 6;
 
 function runTest() {
   window.webkitRequestAnimationFrame(draw);
@@ -18,7 +20,7 @@ function draw() {
   frameCount++;
   var table = document.getElementById("table");
   table.style.backgroundColor = (frameCount & 1) ? 'red' : 'black';
-  if (frameCount == 3) {
+  if (frameCount == totalRafs) {
     domAutomationController.setAutomationId(1);
     domAutomationController.send("FINISHED");
   } else {