Disable Quick View by default and add about flag to enable it.

chrome/app/chromeos_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- ChromeOS-specific strings (included from generated_resources.grd).
      Everything in this file is wrapped in <if expr="chromeos">. -->
 <grit-part>
   <message name="IDS_EMPTY_STRING" desc="Empty string, exist only to make code generic. No translation required.">
   </message>
   <!-- Idle logout dialog for retail mode -->
   <message name="IDS_IDLE_LOGOUT_TITLE" desc="Dialog title for the idle logout dialog. Used in retail mode only.">
     Are you still there?
   </message>
@@ skipping 58 matching lines @@
     The current wallpaper is set by '<ph name="APP_NAME">$1</ph>'. You may need to uninstall '<ph name="APP_NAME">$1</ph>' before selecting a different wallpaper.
   </message>
 
   <!-- File Manager -->
   <message name="IDS_FLAGS_FILE_MANAGER_MTP_NAME" desc="Name of the about:flag option for MTP support in file manager.">
     MTP support in File Manager
   </message>
   <message name="IDS_FLAGS_FILE_MANAGER_MTP_DESCRIPTION" desc="Description of the about:flag option for MTP support in file manager.">
     Show MTP devices as a file storage in the file manager.
   </message>
+  <message name="IDS_FLAGS_FILES_QUICK_VIEW_NAME" desc="Name of the feature flag for files app quick view.">
+    Files app quick view
+  </message>
+  <message name="IDS_FLAGS_FILES_QUICK_VIEW_DESCRIPTION" desc="Description for the feature flag for files app quick view.">
+    Flag for files app quick view, which shows quick preview of a file.
+  </message>
   <message name="IDS_FLAGS_VIDEO_PLAYER_CHROMECAST_SUPPORT_NAME" desc="Name of the about:flag option to enable the chromecast support for video app.">
     Experimental Chromecast support for Video Player
   </message>
   <message name="IDS_FLAGS_VIDEO_PLAYER_CHROMECAST_SUPPORT_DESCRIPTION" desc="Description of the about:flag option to the enable the chromecast support for video app.">
     This option enables experimental Chromecast support for Video Player app on ChromeOS.
   </message>
   <message name="IDS_FLAGS_NEW_ZIP_UNPACKER_NAME" desc="Name of about::flags option for the new ZIP unpacker based on the File System Provider API.">
     New ZIP unpacker
   </message>
   <message name="IDS_FLAGS_NEW_ZIP_UNPACKER_DESCRIPTION" desc="Description of about::flags option for the new ZIP unpacker based on the File System Provider API.">
@@ skipping 6730 matching lines @@
   <message name="IDS_CRITICALLY_LOW_DISK_NOTIFICATION_TITLE" desc="Title of the notification warning users that they are critically low on disk space.">
     Device disk space critically low
   </message>
   <message name="IDS_CRITICALLY_LOW_DISK_NOTIFICATION_MESSAGE" desc="Notification text warning users that they are critically low on disk space.">
     Free up disk space or device will become unresponsive.
   </message>
   <message name="IDS_LOW_DISK_NOTIFICATION_BUTTON" desc="Button on the low disk notification to open storage management.">
     Manage storage
   </message>
 </grit-part>