Files.app: Extract the TextMeasure class to a new file.

chrome/browser/resources/file_manager/js/text_measure.js

+// Copyright 2013 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';
+
+/**
+ * TextMeasure constructor.
+ *
+ * TextMeasure is a measure for text that returns the width of text.  This
+ * class has a dummy span element. When measuring the width of text, it sets
+ * the text to the element and obtains the element's size by
+ * getBoundingClientRect.
+ *
+ * @constructor
+ * @param {HTMLElement} element Element that has styles of measured text. The
+ *     width of text is mesures like as it is rendered in this element.
+ */
+var TextMeasure = function(element) {
+  var doc = element.ownerDocument;
+  this.dummySpan_ = doc.createElement('span');
+  this.dummySpan_ = doc.getElementsByTagName('body')[0].
+                        appendChild(this.dummySpan_);
+  this.dummySpan_.style.position = 'absolute';
+  this.dummySpan_.style.visibility = 'hidden';
+  var styles = window.getComputedStyle(element, '');
+  var stylesToBeCopied = [
+    'fontSize',
+    'fontStyle',
+    'fontWeight',
+    'fontFamily',
+    'letterSpacing'
+  ];
+  for (var i = 0; i < stylesToBeCopied.length; i++) {
+    this.dummySpan_.style[stylesToBeCopied[i]] = styles[stylesToBeCopied[i]];
+  }
+  Object.seal(this);
+};
+
+/**
+ * Measures the widht of text.
+ *
+ * @param {string} text Text that is measured the width.
+ * @return {number} Width of the specified text.
+ */
+TextMeasure.prototype.getWidth = function(text) {
+  this.dummySpan_.innerText = text;
+  var rect = this.dummySpan_.getBoundingClientRect();
+  return rect ? rect.width : 0;
+};