Files.app: Add a deduplication step to avoid importing duplicate media.

ui/file_manager/file_manager/common/js/test_importer_common.js

Index: ui/file_manager/file_manager/common/js/test_importer_common.js
diff --git a/ui/file_manager/file_manager/common/js/test_importer_common.js b/ui/file_manager/file_manager/common/js/test_importer_common.js
new file mode 100644
index 0000000000000000000000000000000000000000..a4618672ef389e6f4813569a3b3e011caff5a979
--- /dev/null
+++ b/ui/file_manager/file_manager/common/js/test_importer_common.js
@@ -0,0 +1,44 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Shared cloud importer namespace
+var importer = importer || {};
+
+/**
+ * Sets up a logger for use in unit tests.  The test logger doesn't attempt to
+ * access chrome's sync file system.  Call this during setUp.
+ */
+importer.setupTestLogger = function() {
+  importer.logger_ = new importer.TestLogger();
+};
+
+/**
+ * A {@code importer.Logger} for testing.  Just sends output to the console.
+ *
+ * @constructor
+ * @implements {importer.Logger}
+ * @struct
+ * @final
+ */
+importer.TestLogger = function() {};
+
+/** @override */
+importer.TestLogger.prototype.info = function(content) {
+  console.log(content);
+};
+
+/** @override */
+importer.TestLogger.prototype.error = function(content) {
+  console.error(content);
+  console.error(new Error('Error stack').stack);
+};
+
+/** @override */
+importer.TestLogger.prototype.catcher = function(context) {
+  return function(error) {
+    this.error('Caught promise error. Context: ' + context +
+        ' Error: ' + error.message);
+    console.error(error.stack);
+  }.bind(this);
+};