Refactor a database test such that its code can be shared between the documen...

LayoutTests/storage/resources/database-worker.js

+var window = {
+  layoutTestController: {
+    notifyDone: function() { postMessage("notifyDone"); }
+  }
+};
+var layoutTestController = window.layoutTestController;
+
+function log(s) {
+  postMessage("log:" + s);
+}
+
+onmessage = function(event) {
+  try {
+    if (event.data.indexOf("importScripts:") == 0) {
+      var scripts = event.data.substring("importScripts:".length).split(",");
+      for (var i in scripts) {
+        scripts[i] = "../" + scripts[i];
+      }
+      importScripts(scripts);
+    } else if (event.data == "runTest") {
+      runTest(); // Must be defined by some imported script.
+    } else {
+      log("Received unexpected message: " + event.data);
+    }
+  } catch (ex) {
+    log("Worker caught exception: " + ex);
+    window.layoutTestController.notifyDone();
+  }
+}