Show a label to describe some invalid drag-drop operations in Files app.

chrome/app/chromeos_strings.grdp

Index: chrome/app/chromeos_strings.grdp
diff --git a/chrome/app/chromeos_strings.grdp b/chrome/app/chromeos_strings.grdp
index 91631a35f0d544c4d2f340f82cd1f79e090830db..301d61a4aaf92fe99d58b2c058ce3fd10eb33cdd 100644
--- a/chrome/app/chromeos_strings.grdp
+++ b/chrome/app/chromeos_strings.grdp
@@ -747,6 +747,12 @@ Press any key to continue exploring.
   <message name="IDS_FILE_BROWSER_SUGGEST_DIALOG_INSTALLATION_FAILED" desc="Error message when the installation of the app from WebStore is failed.">
     Installation failed.
   </message>
+  <message name="IDS_FILE_BROWSER_DROP_TARGET_DEVICE_WRITE_PROTECTED" desc="Tooltip label displayed besides mouse pointer while dragging files or folders over a write-protected folder or disk.">
+    Device is read-only
+  </message>
+  <message name="IDS_FILE_BROWSER_DROP_TARGET_ACCESS_RESTRICTED" desc="Tooltip label displayed besides mouse pointer when dragging files or folders over a removable device whose write access is restricted by administration policy.">
+    Access restricted
+  </message>
 
   <message name="IDS_FILE_BROWSER_SELECT_FOLDER_TITLE" desc="Select folder title.">
     Select a folder to open