compositor-worker: Restrict the global interface in CompositorWorker.

LayoutTests/resources/js-test.js

Index: LayoutTests/resources/js-test.js
diff --git a/LayoutTests/resources/js-test.js b/LayoutTests/resources/js-test.js
index e86533fc2bd1befb5085f7abbadbcc0118352dc5..f30940f8dfc2c0be7bbc8e98adcf900e34660b29 100644
--- a/LayoutTests/resources/js-test.js
+++ b/LayoutTests/resources/js-test.js
@@ -811,11 +811,19 @@ function finishJSTest()
         testRunner.notifyDone();
 }
 
-function startWorker(testScriptURL, shared)
+function startWorker(testScriptURL, workerType)
 {
+    var shared = workerType == 'shared';
+    var compositor = workerType == 'compositor';
     self.jsTestIsAsync = true;
     debug('Starting worker: ' + testScriptURL);
-    var worker = shared ? new SharedWorker(testScriptURL, "Shared Worker") : new Worker(testScriptURL);
+    var worker;
+    if (shared)
+        worker = new SharedWorker(testScriptURL, "Shared Worker");
+    else if (compositor)
+        worker = new CompositorWorker(testScriptURL);
+    else
+        worker = new Worker(testScriptURL);
     worker.onmessage = function(event)
     {
         var workerPrefix = "[Worker] ";