Reland r221579: Files.app: Let the PreviewPanel class control the visibility of the preview panel.

chrome/browser/resources/file_manager/js/ui/preview_panel.js

Index: chrome/browser/resources/file_manager/js/ui/preview_panel.js
diff --git a/chrome/browser/resources/file_manager/js/ui/preview_panel.js b/chrome/browser/resources/file_manager/js/ui/preview_panel.js
index c770ac7a4a5fd7765e46f177a3b778f91854fe95..467fc9e2d956d6acc720b3a74449dcd572cf2783 100644
--- a/chrome/browser/resources/file_manager/js/ui/preview_panel.js
+++ b/chrome/browser/resources/file_manager/js/ui/preview_panel.js
@@ -92,11 +92,11 @@ PreviewPanel.Event = Object.freeze({
  */
 PreviewPanel.VisibilityType = Object.freeze({
   // Preview panel always shows.
-  ALWAYS: 'always',
+  ALWAYS_VISIBLE: 'alwaysVisible',
   // Preview panel shows when the entries property are set.
   AUTO: 'auto',
   // Preview panel does not show.
-  HIDDEN: 'hidden'
+  ALWAYS_HIDDEN: 'alwaysHidden'
 });
 
 /**
@@ -144,6 +144,10 @@ PreviewPanel.prototype = {
         PreviewPanel.Visibility_.VISIBLE;
   },
 
+  /**
+   * Obtains the height of preview panel.
+   * @return {number} Height of preview panel.
+   */
   get height() {
     this.height_ = this.height_ || this.element_.clientHeight;
     return this.height_;
@@ -168,14 +172,14 @@ PreviewPanel.prototype.updateVisibility_ = function() {
   var visibility = this.element_.getAttribute('visibility');
   var newVisible = null;
   switch (this.visibilityType_) {
-    case PreviewPanel.VisibilityType.ALWAYS:
+    case PreviewPanel.VisibilityType.ALWAYS_VISIBLE:
       newVisible = true;
       break;
     case PreviewPanel.VisibilityType.AUTO:
       newVisible = this.entries_.length != 0 ||
                    !PathUtil.isRootPath(this.currentPath_);
       break;
-    case PreviewPanel.VisibilityType.HIDDEN:
+    case PreviewPanel.VisibilityType.ALWAYS_HIDDEN:
       newVisible = false;
       break;
     default: