Revert "Revert of Refactor get_salient_image_url.js to use DocumentImageExtractor"

components/resources/enhanced_bookmarks/get_salient_image_url.js

+// 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.
+
+goog.require('image.collections.extension.domextractor.DocumentImageExtractor');
+
+/*
+ * Examines the DOM to find the image that is the most representative of the
+ * webpage.
+ */
+var GetSalientImageUrl = function() {
+  // Extract the referrer policy from the page.
+  var referrerPolicy = 'default';
+  var metaTags = document.getElementsByTagName('meta');
+  for (var i = 0; i < metaTags.length; i++) {
+    if (metaTags[i].name.toLowerCase() == 'referrer') {
+      referrerPolicy = metaTags[i].content.toLowerCase();
+      break;
+    }
+  }
+
+  // Determine which JSON method (stringify or encode) to use for encoding.
+  // Some pages use a library that overrides JSON, so JSON['stringify'] is not
+  // always available.
+  var jsonEncoder = JSON['stringify'];
+  if (!jsonEncoder)
+    jsonEncoder = JSON['encode'];
+
+  var context = new
+      image.collections.extension.domextractor.DocumentImageExtractor.Context();
+  var documentImageExtractor =
+      new image.collections.extension.domextractor.DocumentImageExtractor();
+  var images = documentImageExtractor.extractFromNodeList(
+      document.querySelectorAll('img,link,meta'), context);
+
+  var maxImage = null;
+  var maxRelevance = 0;
+  for (var i = 0; i < images.length; i++) {
+    var currentImage = images[i];
+    var imageSize = currentImage.getSize();
+    if (!imageSize)
+      continue;
+
+    if (currentImage.getRelevance() > maxRelevance) {
+      maxImage = currentImage;
+      maxRelevance = currentImage.getRelevance();
+    }
+  }
+
+  if (maxImage === null)
+    return '';
+
+  var result = jsonEncoder({
+    'imageUrl': maxImage.getUrl(),
+    'referrerPolicy': referrerPolicy
+  });
+
+  return result;
+};