[Files.app] Split the JavaScript files into subdirectories: common, background, and foreground

chrome/browser/resources/file_manager/js/metadata/metadata_cache.js

-// Copyright (c) 2012 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.
-
-'use strict';
-
-/**
- * MetadataCache is a map from url to an object containing properties.
- * Properties are divided by types, and all properties of one type are accessed
- * at once.
- * Some of the properties:
- * {
- *   filesystem: size, modificationTime
- *   internal: presence
- *   drive: pinned, present, hosted, availableOffline
- *   streaming: (no property)
- *
- *   Following are not fetched for non-present drive files.
- *   media: artist, album, title, width, height, imageTransform, etc.
- *   thumbnail: url, transform
- *
- *   Following are always fetched from content, and so force the downloading
- *   of remote drive files. One should use this for required content metadata,
- *   i.e. image orientation.
- *   fetchedMedia: width, height, etc.
- * }
- *
- * Typical usages:
- * {
- *   cache.get([entry1, entry2], 'drive|filesystem', function(metadata) {
- *     if (metadata[0].drive.pinned && metadata[1].filesystem.size == 0)
- *       alert("Pinned and empty!");
- *   });
- *
- *   cache.set(entry, 'internal', {presence: 'deleted'});
- *
- *   cache.clear([fileUrl1, fileUrl2], 'filesystem');
- *
- *   // Getting fresh value.
- *   cache.clear(entry, 'thumbnail');
- *   cache.get(entry, 'thumbnail', function(thumbnail) {
- *     img.src = thumbnail.url;
- *   });
- *
- *   var cached = cache.getCached(entry, 'filesystem');
- *   var size = (cached && cached.size) || UNKNOWN_SIZE;
- * }
- *
- * @constructor
- */
-function MetadataCache() {
-  /**
-   * Map from urls to entries. Entry contains |properties| - an hierarchical
-   * object of values, and an object for each metadata provider:
-   * <prodiver-id>: { time, callbacks }
-   * @private
-   */
-  this.cache_ = {};
-
-  /**
-   * List of metadata providers.
-   * @private
-   */
-  this.providers_ = [];
-
-  /**
-   * List of observers added. Each one is an object with fields:
-   *   re - regexp of urls;
-   *   type - metadata type;
-   *   callback - the callback.
-   * TODO(dgozman): pass entries to observer if present.
-   * @private
-   */
-  this.observers_ = [];
-  this.observerId_ = 0;
-
-  this.batchCount_ = 0;
-  this.totalCount_ = 0;
-
-  /**
-   * Time of first get query of the current batch. Items updated later than this
-   * will not be evicted.
-   * @private
-   */
-  this.lastBatchStart_ = new Date();
-}
-
-/**
- * Observer type: it will be notified if the url changed is exactly the same
- * as the url passed.
- */
-MetadataCache.EXACT = 0;
-
-/**
- * Observer type: it will be notified if the url changed is an immediate child
- * of the url passed.
- */
-MetadataCache.CHILDREN = 1;
-
-/**
- * Observer type: it will be notified if the url changed is any descendant
- * of the url passed.
- */
-MetadataCache.DESCENDANTS = 2;
-
-/**
- * Minimum number of items in cache to start eviction.
- */
-MetadataCache.EVICTION_NUMBER = 1000;
-
-/**
- * @return {MetadataCache!} The cache with all providers.
- */
-MetadataCache.createFull = function() {
-  var cache = new MetadataCache();
-  cache.providers_.push(new FilesystemProvider());
-  cache.providers_.push(new DriveProvider());
-  cache.providers_.push(new ContentProvider());
-  return cache;
-};
-
-/**
- * Clones metadata entry. Metadata entries may contain scalars, arrays,
- * hash arrays and Date object. Other objects are not supported.
- * @param {Object} metadata Metadata object.
- * @return {Object} Cloned entry.
- */
-MetadataCache.cloneMetadata = function(metadata) {
-  if (metadata instanceof Array) {
-    var result = [];
-    for (var index = 0; index < metadata.length; index++) {
-      result[index] = MetadataCache.cloneMetadata(metadata[index]);
-    }
-    return result;
-  } else if (metadata instanceof Date) {
-    var result = new Date();
-    result.setTime(metadata.getTime());
-    return result;
-  } else if (metadata instanceof Object) {  // Hash array only.
-    var result = {};
-    for (var property in metadata) {
-      if (metadata.hasOwnProperty(property))
-        result[property] = MetadataCache.cloneMetadata(metadata[property]);
-    }
-    return result;
-  } else {
-    return metadata;
-  }
-};
-
-/**
- * @return {boolean} Whether all providers are ready.
- */
-MetadataCache.prototype.isInitialized = function() {
-  for (var index = 0; index < this.providers_.length; index++) {
-    if (!this.providers_[index].isInitialized()) return false;
-  }
-  return true;
-};
-
-/**
- * Fetches the metadata, puts it in the cache, and passes to callback.
- * If required metadata is already in the cache, does not fetch it again.
- * @param {string|Entry|Array.<string|Entry>} items The list of entries or
- *     file urls. May be just a single item.
- * @param {string} type The metadata type.
- * @param {function(Object)} callback The metadata is passed to callback.
- */
-MetadataCache.prototype.get = function(items, type, callback) {
-  if (!(items instanceof Array)) {
-    this.getOne(items, type, callback);
-    return;
-  }
-
-  if (items.length == 0) {
-    if (callback) callback([]);
-    return;
-  }
-
-  var result = [];
-  var remaining = items.length;
-  this.startBatchUpdates();
-
-  var onOneItem = function(index, value) {
-    result[index] = value;
-    remaining--;
-    if (remaining == 0) {
-      this.endBatchUpdates();
-      if (callback) setTimeout(callback, 0, result);
-    }
-  };
-
-  for (var index = 0; index < items.length; index++) {
-    result.push(null);
-    this.getOne(items[index], type, onOneItem.bind(this, index));
-  }
-};
-
-/**
- * Fetches the metadata for one Entry/FileUrl. See comments to |get|.
- * @param {Entry|string} item The entry or url.
- * @param {string} type Metadata type.
- * @param {function(Object)} callback The callback.
- */
-MetadataCache.prototype.getOne = function(item, type, callback) {
-  if (type.indexOf('|') != -1) {
-    var types = type.split('|');
-    var result = {};
-    var typesLeft = types.length;
-
-    var onOneType = function(requestedType, metadata) {
-      result[requestedType] = metadata;
-      typesLeft--;
-      if (typesLeft == 0) callback(result);
-    };
-
-    for (var index = 0; index < types.length; index++) {
-      this.getOne(item, types[index], onOneType.bind(null, types[index]));
-    }
-    return;
-  }
-
-  var url = this.itemToUrl_(item);
-
-  // Passing entry to fetchers may save one round-trip to APIs.
-  var fsEntry = item === url ? null : item;
-  callback = callback || function() {};
-
-  if (!(url in this.cache_)) {
-    this.cache_[url] = this.createEmptyEntry_();
-    this.totalCount_++;
-  }
-
-  var entry = this.cache_[url];
-
-  if (type in entry.properties) {
-    callback(entry.properties[type]);
-    return;
-  }
-
-  this.startBatchUpdates();
-  var providers = this.providers_.slice();
-  var currentProvider;
-  var self = this;
-
-  var onFetched = function() {
-    if (type in entry.properties) {
-      self.endBatchUpdates();
-      // Got properties from provider.
-      callback(entry.properties[type]);
-    } else {
-      tryNextProvider();
-    }
-  };
-
-  var onProviderProperties = function(properties) {
-    var id = currentProvider.getId();
-    var fetchedCallbacks = entry[id].callbacks;
-    delete entry[id].callbacks;
-    entry.time = new Date();
-    self.mergeProperties_(url, properties);
-
-    for (var index = 0; index < fetchedCallbacks.length; index++) {
-      fetchedCallbacks[index]();
-    }
-  };
-
-  var queryProvider = function() {
-    var id = currentProvider.getId();
-    if ('callbacks' in entry[id]) {
-      // We are querying this provider now.
-      entry[id].callbacks.push(onFetched);
-    } else {
-      entry[id].callbacks = [onFetched];
-      currentProvider.fetch(url, type, onProviderProperties, fsEntry);
-    }
-  };
-
-  var tryNextProvider = function() {
-    if (providers.length == 0) {
-      self.endBatchUpdates();
-      callback(entry.properties[type] || null);
-      return;
-    }
-
-    currentProvider = providers.shift();
-    if (currentProvider.supportsUrl(url) &&
-        currentProvider.providesType(type)) {
-      queryProvider();
-    } else {
-      tryNextProvider();
-    }
-  };
-
-  tryNextProvider();
-};
-
-/**
- * Returns the cached metadata value, or |null| if not present.
- * @param {string|Entry|Array.<string|Entry>} items The list of entries or
- *     file urls. May be just a single item.
- * @param {string} type The metadata type.
- * @return {Object} The metadata or null.
- */
-MetadataCache.prototype.getCached = function(items, type) {
-  var single = false;
-  if (!(items instanceof Array)) {
-    single = true;
-    items = [items];
-  }
-
-  var result = [];
-  for (var index = 0; index < items.length; index++) {
-    var url = this.itemToUrl_(items[index]);
-    result.push(url in this.cache_ ?
-        (this.cache_[url].properties[type] || null) : null);
-  }
-
-  return single ? result[0] : result;
-};
-
-/**
- * Puts the metadata into cache
- * @param {string|Entry|Array.<string|Entry>} items The list of entries or
- *     file urls. May be just a single item.
- * @param {string} type The metadata type.
- * @param {Array.<Object>} values List of corresponding metadata values.
- */
-MetadataCache.prototype.set = function(items, type, values) {
-  if (!(items instanceof Array)) {
-    items = [items];
-    values = [values];
-  }
-
-  this.startBatchUpdates();
-  for (var index = 0; index < items.length; index++) {
-    var url = this.itemToUrl_(items[index]);
-    if (!(url in this.cache_)) {
-      this.cache_[url] = this.createEmptyEntry_();
-      this.totalCount_++;
-    }
-    this.cache_[url].properties[type] = values[index];
-    this.notifyObservers_(url, type);
-  }
-  this.endBatchUpdates();
-};
-
-/**
- * Clears the cached metadata values.
- * @param {string|Entry|Array.<string|Entry>} items The list of entries or
- *     file urls. May be just a single item.
- * @param {string} type The metadata types or * for any type.
- */
-MetadataCache.prototype.clear = function(items, type) {
-  if (!(items instanceof Array))
-    items = [items];
-
-  var types = type.split('|');
-
-  for (var index = 0; index < items.length; index++) {
-    var url = this.itemToUrl_(items[index]);
-    if (url in this.cache_) {
-      if (type === '*') {
-        this.cache_[url].properties = {};
-      } else {
-        for (var j = 0; j < types.length; j++) {
-          var type = types[j];
-          delete this.cache_[url].properties[type];
-        }
-      }
-    }
-  }
-};
-
-/**
- * Clears the cached metadata values recursively.
- * @param {Entry|string} item An entry or a url.
- * @param {string} type The metadata types or * for any type.
- */
-MetadataCache.prototype.clearRecursively = function(item, type) {
-  var types = type.split('|');
-  var keys = Object.keys(this.cache_);
-  var url = this.itemToUrl_(item);
-
-  for (var index = 0; index < keys.length; index++) {
-    var entryUrl = keys[index];
-    if (entryUrl.substring(0, url.length) === url) {
-      if (type === '*') {
-        this.cache_[entryUrl].properties = {};
-      } else {
-        for (var j = 0; j < types.length; j++) {
-          var type = types[j];
-          delete this.cache_[entryUrl].properties[type];
-        }
-      }
-    }
-  }
-};
-
-/**
- * Adds an observer, which will be notified when metadata changes.
- * @param {string|Entry} item The root item to look at.
- * @param {number} relation This defines, which items will trigger the observer.
- *     See comments to |MetadataCache.EXACT| and others.
- * @param {string} type The metadata type.
- * @param {function(Array.<string>, Array.<Object>)} observer List of file urls
- *     and corresponding metadata values are passed to this callback.
- * @return {number} The observer id, which can be used to remove it.
- */
-MetadataCache.prototype.addObserver = function(item, relation, type, observer) {
-  var url = this.itemToUrl_(item);
-  var re = url;
-  if (relation == MetadataCache.CHILDREN) {
-    re += '(/[^/]*)?';
-  } else if (relation == MetadataCache.DESCENDANTS) {
-    re += '(/.*)?';
-  }
-  var id = ++this.observerId_;
-  this.observers_.push({
-    re: new RegExp('^' + re + '$'),
-    type: type,
-    callback: observer,
-    id: id,
-    pending: {}
-  });
-  return id;
-};
-
-/**
- * Removes the observer.
- * @param {number} id Observer id.
- * @return {boolean} Whether observer was removed or not.
- */
-MetadataCache.prototype.removeObserver = function(id) {
-  for (var index = 0; index < this.observers_.length; index++) {
-    if (this.observers_[index].id == id) {
-      this.observers_.splice(index, 1);
-      return true;
-    }
-  }
-  return false;
-};
-
-/**
- * Start batch updates.
- */
-MetadataCache.prototype.startBatchUpdates = function() {
-  this.batchCount_++;
-  if (this.batchCount_ == 1)
-    this.lastBatchStart_ = new Date();
-};
-
-/**
- * End batch updates. Notifies observers if all nested updates are finished.
- */
-MetadataCache.prototype.endBatchUpdates = function() {
-  this.batchCount_--;
-  if (this.batchCount_ != 0) return;
-  if (this.totalCount_ > MetadataCache.EVICTION_NUMBER)
-    this.evict_();
-  for (var index = 0; index < this.observers_.length; index++) {
-    var observer = this.observers_[index];
-    var urls = [];
-    var properties = [];
-    for (var url in observer.pending) {
-      if (observer.pending.hasOwnProperty(url) && url in this.cache_) {
-        urls.push(url);
-        properties.push(this.cache_[url].properties[observer.type] || null);
-      }
-    }
-    observer.pending = {};
-    if (urls.length > 0) {
-      observer.callback(urls, properties);
-    }
-  }
-};
-
-/**
- * Notifies observers or puts the data to pending list.
- * @param {string} url Url of entry changed.
- * @param {string} type Metadata type.
- * @private
- */
-MetadataCache.prototype.notifyObservers_ = function(url, type) {
-  for (var index = 0; index < this.observers_.length; index++) {
-    var observer = this.observers_[index];
-    if (observer.type == type && observer.re.test(url)) {
-      if (this.batchCount_ == 0) {
-        // Observer expects array of urls and array of properties.
-        observer.callback([url], [this.cache_[url].properties[type] || null]);
-      } else {
-        observer.pending[url] = true;
-      }
-    }
-  }
-};
-
-/**
- * Removes the oldest items from the cache.
- * This method never removes the items from last batch.
- * @private
- */
-MetadataCache.prototype.evict_ = function() {
-  var toRemove = [];
-
-  // We leave only a half of items, so we will not call evict_ soon again.
-  var desiredCount = Math.round(MetadataCache.EVICTION_NUMBER / 2);
-  var removeCount = this.totalCount_ - desiredCount;
-  for (var url in this.cache_) {
-    if (this.cache_.hasOwnProperty(url) &&
-        this.cache_[url].time < this.lastBatchStart_) {
-      toRemove.push(url);
-    }
-  }
-
-  toRemove.sort(function(a, b) {
-    var aTime = this.cache_[a].time;
-    var bTime = this.cache_[b].time;
-    return aTime < bTime ? -1 : aTime > bTime ? 1 : 0;
-  }.bind(this));
-
-  removeCount = Math.min(removeCount, toRemove.length);
-  this.totalCount_ -= removeCount;
-  for (var index = 0; index < removeCount; index++) {
-    delete this.cache_[toRemove[index]];
-  }
-};
-
-/**
- * Converts Entry or file url to url.
- * @param {string|Entry} item Item to convert.
- * @return {string} File url.
- * @private
- */
-MetadataCache.prototype.itemToUrl_ = function(item) {
-  if (typeof(item) == 'string')
-    return item;
-
-  if (!item._URL_) {
-    // Is a fake entry.
-    if (typeof item.toURL !== 'function')
-      item._URL_ = util.makeFilesystemUrl(item.fullPath);
-    else
-      item._URL_ = item.toURL();
-  }
-
-  return item._URL_;
-};
-
-/**
- * @return {Object} Empty cache entry.
- * @private
- */
-MetadataCache.prototype.createEmptyEntry_ = function() {
-  var entry = {properties: {}};
-  for (var index = 0; index < this.providers_.length; index++) {
-    entry[this.providers_[index].getId()] = {};
-  }
-  return entry;
-};
-
-/**
- * Caches all the properties from data to cache entry for url.
- * @param {string} url The url.
- * @param {Object} data The properties.
- * @private
- */
-MetadataCache.prototype.mergeProperties_ = function(url, data) {
-  if (data == null) return;
-  var properties = this.cache_[url].properties;
-  for (var type in data) {
-    if (data.hasOwnProperty(type) && !properties.hasOwnProperty(type)) {
-      properties[type] = data[type];
-      this.notifyObservers_(url, type);
-    }
-  }
-};
-
-/**
- * Base class for metadata providers.
- * @constructor
- */
-function MetadataProvider() {
-}
-
-/**
- * @param {string} url The url.
- * @return {boolean} Whether this provider supports the url.
- */
-MetadataProvider.prototype.supportsUrl = function(url) { return false; };
-
-/**
- * @param {string} type The metadata type.
- * @return {boolean} Whether this provider provides this metadata.
- */
-MetadataProvider.prototype.providesType = function(type) { return false; };
-
-/**
- * @return {string} Unique provider id.
- */
-MetadataProvider.prototype.getId = function() { return ''; };
-
-/**
- * @return {boolean} Whether provider is ready.
- */
-MetadataProvider.prototype.isInitialized = function() { return true; };
-
-/**
- * Fetches the metadata. It's suggested to return all the metadata this provider
- * can fetch at once.
- * @param {string} url File url.
- * @param {string} type Requested metadata type.
- * @param {function(Object)} callback Callback expects a map from metadata type
- *     to metadata value.
- * @param {Entry=} opt_entry The file entry if present.
- */
-MetadataProvider.prototype.fetch = function(url, type, callback, opt_entry) {
-  throw new Error('Default metadata provider cannot fetch.');
-};
-
-
-/**
- * Provider of filesystem metadata.
- * This provider returns the following objects:
- * filesystem: { size, modificationTime }
- * @constructor
- */
-function FilesystemProvider() {
-  MetadataProvider.call(this);
-}
-
-FilesystemProvider.prototype = {
-  __proto__: MetadataProvider.prototype
-};
-
-/**
- * @param {string} url The url.
- * @return {boolean} Whether this provider supports the url.
- */
-FilesystemProvider.prototype.supportsUrl = function(url) {
-  return true;
-};
-
-/**
- * @param {string} type The metadata type.
- * @return {boolean} Whether this provider provides this metadata.
- */
-FilesystemProvider.prototype.providesType = function(type) {
-  return type == 'filesystem';
-};
-
-/**
- * @return {string} Unique provider id.
- */
-FilesystemProvider.prototype.getId = function() { return 'filesystem'; };
-
-/**
- * Fetches the metadata.
- * @param {string} url File url.
- * @param {string} type Requested metadata type.
- * @param {function(Object)} callback Callback expects a map from metadata type
- *     to metadata value.
- * @param {Entry=} opt_entry The file entry if present.
- */
-FilesystemProvider.prototype.fetch = function(url, type, callback, opt_entry) {
-  function onError(error) {
-    callback(null);
-  }
-
-  function onMetadata(entry, metadata) {
-    callback({
-      filesystem: {
-        size: entry.isFile ? (metadata.size || 0) : -1,
-        modificationTime: metadata.modificationTime
-      }
-    });
-  }
-
-  function onEntry(entry) {
-    entry.getMetadata(onMetadata.bind(null, entry), onError);
-  }
-
-  if (opt_entry)
-    onEntry(opt_entry);
-  else
-    window.webkitResolveLocalFileSystemURL(url, onEntry, onError);
-};
-
-/**
- * Provider of drive metadata.
- * This provider returns the following objects:
- *     drive: { pinned, hosted, present, customIconUrl, etc. }
- *     thumbnail: { url, transform }
- *     streaming: { }
- * @constructor
- */
-function DriveProvider() {
-  MetadataProvider.call(this);
-
-  // We batch metadata fetches into single API call.
-  this.urls_ = [];
-  this.callbacks_ = [];
-  this.scheduled_ = false;
-
-  this.callApiBound_ = this.callApi_.bind(this);
-}
-
-DriveProvider.prototype = {
-  __proto__: MetadataProvider.prototype
-};
-
-/**
- * @param {string} url The url.
- * @return {boolean} Whether this provider supports the url.
- */
-DriveProvider.prototype.supportsUrl = function(url) {
-  return FileType.isOnDrive(url);
-};
-
-/**
- * @param {string} type The metadata type.
- * @return {boolean} Whether this provider provides this metadata.
- */
-DriveProvider.prototype.providesType = function(type) {
-  return type == 'drive' || type == 'thumbnail' ||
-      type == 'streaming' || type == 'media';
-};
-
-/**
- * @return {string} Unique provider id.
- */
-DriveProvider.prototype.getId = function() { return 'drive'; };
-
-/**
- * Fetches the metadata.
- * @param {string} url File url.
- * @param {string} type Requested metadata type.
- * @param {function(Object)} callback Callback expects a map from metadata type
- *     to metadata value.
- * @param {Entry=} opt_entry The file entry if present.
- */
-DriveProvider.prototype.fetch = function(url, type, callback, opt_entry) {
-  this.urls_.push(url);
-  this.callbacks_.push(callback);
-  if (!this.scheduled_) {
-    this.scheduled_ = true;
-    setTimeout(this.callApiBound_, 0);
-  }
-};
-
-/**
- * Schedules the API call.
- * @private
- */
-DriveProvider.prototype.callApi_ = function() {
-  this.scheduled_ = false;
-
-  var urls = this.urls_;
-  var callbacks = this.callbacks_;
-  this.urls_ = [];
-  this.callbacks_ = [];
-  var self = this;
-
-  var task = function(url, callback) {
-    chrome.fileBrowserPrivate.getDriveEntryProperties(url,
-        function(properties) {
-          callback(self.convert_(properties, url));
-        });
-  };
-
-  for (var i = 0; i < urls.length; i++)
-    task(urls[i], callbacks[i]);
-};
-
-/**
- * @param {DriveEntryProperties} data Drive entry properties.
- * @param {string} url File url.
- * @return {boolean} True if the file is available offline.
- */
-DriveProvider.isAvailableOffline = function(data, url) {
-  if (data.isPresent)
-    return true;
-
-  if (!data.isHosted)
-    return false;
-
-  // What's available offline? See the 'Web' column at:
-  // http://support.google.com/drive/bin/answer.py?hl=en&answer=1628467
-  var subtype = FileType.getType(url).subtype;
-  return (subtype == 'doc' ||
-          subtype == 'draw' ||
-          subtype == 'sheet' ||
-          subtype == 'slides');
-};
-
-/**
- * @param {DriveEntryProperties} data Drive entry properties.
- * @return {boolean} True if opening the file does not require downloading it
- *    via a metered connection.
- */
-DriveProvider.isAvailableWhenMetered = function(data) {
-  return data.isPresent || data.isHosted;
-};
-
-/**
- * Converts API metadata to internal format.
- * @param {Object} data Metadata from API call.
- * @param {string} url File url.
- * @return {Object} Metadata in internal format.
- * @private
- */
-DriveProvider.prototype.convert_ = function(data, url) {
-  var result = {};
-  result.drive = {
-    present: data.isPresent,
-    pinned: data.isPinned,
-    hosted: data.isHosted,
-    imageWidth: data.imageWidth,
-    imageHeight: data.imageHeight,
-    imageRotation: data.imageRotation,
-    availableOffline: DriveProvider.isAvailableOffline(data, url),
-    availableWhenMetered: DriveProvider.isAvailableWhenMetered(data),
-    customIconUrl: data.customIconUrl || '',
-    contentMimeType: data.contentMimeType || '',
-    sharedWithMe: data.sharedWithMe
-  };
-
-  if (!data.isPresent) {
-    // Block the local fetch for drive files, which require downloading.
-    result.thumbnail = {url: '', transform: null};
-    result.media = {};
-  }
-
-  if ('thumbnailUrl' in data) {
-    result.thumbnail = {
-      url: data.thumbnailUrl.replace(/s220/, 's500'),
-      transform: null
-    };
-  }
-  if (!data.isPresent) {
-    // Indicate that the data is not available in local cache.
-    // It used to have a field 'url' for streaming play, but it is
-    // derprecated. See crbug.com/174560.
-    result.streaming = {};
-  }
-  return result;
-};
-
-
-/**
- * Provider of content metadata.
- * This provider returns the following objects:
- * thumbnail: { url, transform }
- * media: { artist, album, title, width, height, imageTransform, etc. }
- * fetchedMedia: { same fields here }
- * @constructor
- */
-function ContentProvider() {
-  MetadataProvider.call(this);
-
-  // Pass all URLs to the metadata reader until we have a correct filter.
-  this.urlFilter_ = /.*/;
-
-  var path = document.location.pathname;
-  var workerPath = document.location.origin +
-      path.substring(0, path.lastIndexOf('/') + 1) +
-      'js/metadata/metadata_dispatcher.js';
-
-  if (ContentProvider.USE_SHARED_WORKER) {
-    this.dispatcher_ = new SharedWorker(workerPath).port;
-    this.dispatcher_.start();
-  } else {
-    this.dispatcher_ = new Worker(workerPath);
-  }
-
-  this.dispatcher_.onmessage = this.onMessage_.bind(this);
-  this.dispatcher_.postMessage({verb: 'init'});
-
-  // Initialization is not complete until the Worker sends back the
-  // 'initialized' message.  See below.
-  this.initialized_ = false;
-
-  // Map from url to callback.
-  // Note that simultaneous requests for same url are handled in MetadataCache.
-  this.callbacks_ = {};
-}
-
-/**
- * Flag defining which kind of a worker to use.
- * TODO(kaznacheev): Observe for some time and remove if SharedWorker does not
- * cause any problems.
- */
-ContentProvider.USE_SHARED_WORKER = true;
-
-ContentProvider.prototype = {
-  __proto__: MetadataProvider.prototype
-};
-
-/**
- * @param {string} url The url.
- * @return {boolean} Whether this provider supports the url.
- */
-ContentProvider.prototype.supportsUrl = function(url) {
-  return url.match(this.urlFilter_);
-};
-
-/**
- * @param {string} type The metadata type.
- * @return {boolean} Whether this provider provides this metadata.
- */
-ContentProvider.prototype.providesType = function(type) {
-  return type == 'thumbnail' || type == 'fetchedMedia' || type == 'media';
-};
-
-/**
- * @return {string} Unique provider id.
- */
-ContentProvider.prototype.getId = function() { return 'content'; };
-
-/**
- * Fetches the metadata.
- * @param {string} url File url.
- * @param {string} type Requested metadata type.
- * @param {function(Object)} callback Callback expects a map from metadata type
- *     to metadata value.
- * @param {Entry=} opt_entry The file entry if present.
- */
-ContentProvider.prototype.fetch = function(url, type, callback, opt_entry) {
-  if (opt_entry && opt_entry.isDirectory) {
-    callback({});
-    return;
-  }
-  this.callbacks_[url] = callback;
-  this.dispatcher_.postMessage({verb: 'request', arguments: [url]});
-};
-
-/**
- * Dispatch a message from a metadata reader to the appropriate on* method.
- * @param {Object} event The event.
- * @private
- */
-ContentProvider.prototype.onMessage_ = function(event) {
-  var data = event.data;
-
-  var methodName =
-      'on' + data.verb.substr(0, 1).toUpperCase() + data.verb.substr(1) + '_';
-
-  if (!(methodName in this)) {
-    console.error('Unknown message from metadata reader: ' + data.verb, data);
-    return;
-  }
-
-  this[methodName].apply(this, data.arguments);
-};
-
-/**
- * @return {boolean} Whether provider is ready.
- */
-ContentProvider.prototype.isInitialized = function() {
-  return this.initialized_;
-};
-
-/**
- * Handles the 'initialized' message from the metadata reader Worker.
- * @param {Object} regexp Regexp of supported urls.
- * @private
- */
-ContentProvider.prototype.onInitialized_ = function(regexp) {
-  this.urlFilter_ = regexp;
-
-  // Tests can monitor for this state with
-  // ExtensionTestMessageListener listener("worker-initialized");
-  // ASSERT_TRUE(listener.WaitUntilSatisfied());
-  // Automated tests need to wait for this, otherwise we crash in
-  // browser_test cleanup because the worker process still has
-  // URL requests in-flight.
-  var test = chrome.test || window.top.chrome.test;
-  test.sendMessage('worker-initialized');
-  this.initialized_ = true;
-};
-
-/**
- * Converts content metadata from parsers to the internal format.
- * @param {Object} metadata The content metadata.
- * @param {Object=} opt_result The internal metadata object ot put result in.
- * @return {Object!} Converted metadata.
- */
-ContentProvider.ConvertContentMetadata = function(metadata, opt_result) {
-  var result = opt_result || {};
-
-  if ('thumbnailURL' in metadata) {
-    metadata.thumbnailTransform = metadata.thumbnailTransform || null;
-    result.thumbnail = {
-      url: metadata.thumbnailURL,
-      transform: metadata.thumbnailTransform
-    };
-  }
-
-  for (var key in metadata) {
-    if (metadata.hasOwnProperty(key)) {
-      if (!('media' in result)) result.media = {};
-      result.media[key] = metadata[key];
-    }
-  }
-
-  if ('media' in result) {
-    result.fetchedMedia = result.media;
-  }
-
-  return result;
-};
-
-/**
- * Handles the 'result' message from the worker.
- * @param {string} url File url.
- * @param {Object} metadata The metadata.
- * @private
- */
-ContentProvider.prototype.onResult_ = function(url, metadata) {
-  var callback = this.callbacks_[url];
-  delete this.callbacks_[url];
-  callback(ContentProvider.ConvertContentMetadata(metadata));
-};
-
-/**
- * Handles the 'error' message from the worker.
- * @param {string} url File url.
- * @param {string} step Step failed.
- * @param {string} error Error description.
- * @param {Object?} metadata The metadata, if available.
- * @private
- */
-ContentProvider.prototype.onError_ = function(url, step, error, metadata) {
-  if (MetadataCache.log)  // Avoid log spam by default.
-    console.warn('metadata: ' + url + ': ' + step + ': ' + error);
-  metadata = metadata || {};
-  // Prevent asking for thumbnail again.
-  metadata.thumbnailURL = '';
-  this.onResult_(url, metadata);
-};
-
-/**
- * Handles the 'log' message from the worker.
- * @param {Array.<*>} arglist Log arguments.
- * @private
- */
-ContentProvider.prototype.onLog_ = function(arglist) {
-  if (MetadataCache.log)  // Avoid log spam by default.
-    console.log.apply(console, ['metadata:'].concat(arglist));
-};