[compositorworker] compositor proxy mutation updates underlying layers

third_party/WebKit/LayoutTests/virtual/threaded/fast/compositorworker/resources/basic-plumbing-main-to-worker.js

+self.onmessage = function(e) {
+  if (e.data.proxy)
+    self.proxy = e.data.proxy;
+  var respond = function(timestamp) {
+    if (!self.proxy.initialized) {
+      requestAnimationFrame(respond);
+      return;
+    }
+    var keys = ['opacity', 'scrollTop', 'scrollLeft'];
+    var values = {};
+    for (var i = 0; i < keys.length; i++) {
+      values[keys[i]] = self.proxy[keys[i]];
+    }
+    values.transform = self.proxy.transform.toFloat32Array();
+    self.postMessage(values);
+  };
+  requestAnimationFrame(respond);
+}