Make chrome.fileManagerPrivate.getSizeStat return actual available space for Downloads.

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 1125 matching lines @@
   </message>
   <message name="IDS_FILE_BROWSER_TIME_YESTERDAY" desc="File date and time in case the date is yesterday.">
     Yesterday <ph name="YESTERDAY_DAYTIME">$1<ex>4:48 PM</ex></ph>
   </message>
 
   <message name="IDS_FILE_BROWSER_ALL_FILES_FILTER" desc="All Files filter for Open/Save dialog">
     All files
   </message>
 
   <message name="IDS_FILE_BROWSER_SPACE_AVAILABLE" desc="Menu item showing space left for storage.">
-    <ph name="SPACE_AVAILABLE">$1<ex>4.8 GB</ex></ph> left
+    <ph name="SPACE_AVAILABLE">$1<ex>4.8 GB</ex></ph> available

[fukino, 2016/08/25 08:00:23]

This label is updated to be consistent with the term in storage manager.

   </message>
   <message name="IDS_FILE_BROWSER_WAITING_FOR_SPACE_INFO" desc="Menu item, saying that FileBrowser is waiting for space information for storage. When actual data arrives, this item will be replaced with IDS_FILE_BROWSER_SPACE_AVAILABLE">
     Waiting for space info...
   </message>
   <message name="IDS_FILE_BROWSER_FAILED_SPACE_INFO" desc="Menu item, saying that FileBrowser is failed to retrieve space information.">
     Failed to retrieve space info
   </message>
 
 <!-- Common for Audio player and Media player -->
   <message name="IDS_MEDIA_PLAYER_PLAY_BUTTON_LABEL" desc="Label for the Play button of media players (audio player / video player).">
@@ skipping 5224 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>