Files.app: Create unit tests for MetadataCache.

chrome/test/data/file_manager/unit_tests/mocks/mock_file_entry.js

Index: chrome/test/data/file_manager/unit_tests/mocks/mock_file_entry.js
diff --git a/chrome/test/data/file_manager/unit_tests/mocks/mock_file_entry.js b/chrome/test/data/file_manager/unit_tests/mocks/mock_file_entry.js
index f1cbce349dc85a611ef105405a85234e0915dd8f..c16a63d395716d4dfe9ff4dbc8ad5ad327481ff5 100644
--- a/chrome/test/data/file_manager/unit_tests/mocks/mock_file_entry.js
+++ b/chrome/test/data/file_manager/unit_tests/mocks/mock_file_entry.js
@@ -13,3 +13,12 @@ function MockFileEntry(volumeId, fullPath) {
   this.volumeId = volumeId;
   this.fullPath = fullPath;
 }
+
+/**
+ * Returns fake URL.
+ *
+ * @return {string} Fake URL.
+ */
+MockFileEntry.prototype.toURL = function() {
+  return 'filesystem:' + this.volumeId + this.fullPath;
+};