Make cloning of File objects more useful.

LayoutTests/fast/files/workers/resources/worker-read-file-constructor-async.js

+importScripts("../../resources/read-common.js")
+
+function log(message)
+{
+    postMessage(message);
+}
+
+function readFiles(index, files)
+{
+    if (index >= files.length) {
+        log("DONE");
+        return;
+    }
+
+    log("Reading: '" + files[index].name + "'");
+    log("Last modified: '" + (new Date(files[index].lastModified)).toUTCString() + "'");
+
+    var reader = new FileReader();
+    var isText = files[index].type.indexOf("text") > -1;
+    reader.onload = function (e) {
+        if (isText) {
+            log("Contents: '" + reader.result + "'");
+            log("Length: " + reader.result.length);
+        } else
+            log("Length: " + reader.result.byteLength);
+        readFiles(index + 1, files);
+    };
+    if (isText)
+        reader.readAsText(files[index]);
+    else
+        reader.readAsArrayBuffer(files[index])
+}
+
+onmessage = function (e) {
+    log('Received files in worker');
+    readFiles(0, e.data);
+};