Files.app: Move the position of dummy element for measuring the size of text.

BUG=392981
TEST=manually

Review URL: https://codereview.chromium.org/419063004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285536 0039d316-1c4b-4281-b951-d872f2087c98

ui/file_manager/file_manager/foreground/css/file_manager.css

@@ -3,6 +3,7 @@
  * found in the LICENSE file. */
 
 /* The order of z-index:
+ * - -1: text-measure
  * - 2: drag-selection-border
  * - 3: preview-panel
  * - 500: scrollbar
@@ -1964,3 +1965,11 @@ menuitem#thumbnail-view[lead]:not([disabled]) {
 #progress-center li:not(.cancelable) button.cancel {
   visibility: hidden;
 }
+
+.text-measure {
+  pointer-events: none;
+  position: absolute;
+  top: 0;
+  visibility: hidden;
+  z-index: -1;
+}

ui/file_manager/file_manager/foreground/js/text_measure.js

@@ -17,26 +17,29 @@
  *     width of text is measures 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';
+  this.dummySpan_ = createElementWithClassName('span', 'text-measure');
   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]];
+  for (var i = 0; i < TextMeasure.STYLES_TO_BE_COPYED.length; i++) {
+    var name = TextMeasure.STYLES_TO_BE_COPYED[i];
+    this.dummySpan_.style[name] = styles[name];
   }
+  element.ownerDocument.body.appendChild(this.dummySpan_);
   Object.seal(this);
 };
 
+/**
+ * Style names to be copied to the measured dummy span.
+ * @type {Array.<String>}
+ * @const
+ */
+TextMeasure.STYLES_TO_BE_COPYED = Object.freeze([
+  'fontSize',
+  'fontStyle',
+  'fontWeight',
+  'fontFamily',
+  'letterSpacing'
+]);
+
 /**
  * Measures the width of text.
  *