[Mac] Update Quit notification strings.

chrome/app/chromium_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 <!-- This file contains definitions of strings that are distribution specific.
 These strings will not be translated and only english versions will
 be available for now. -->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
       source_lang_id="en" enc_check="möl">
   <outputs>
     <output filename="grit/chromium_strings.h" type="rc_header">
       <emit emit_type='prepend'></emit>
@@ skipping 644 matching lines @@
       <message name="IDS_MULTIPLE_DOWNLOADS_REMOVE_CONFIRM_EXPLANATION" desc="Explanation of the dialog asking for user confirmation to close the browser when multiple downloads are in progress.">
         Downloads are currently in progress. Do you want to exit Chromium and cancel the downloads?
       </message>
       <message name="IDS_DOWNLOAD_REMOVE_CONFIRM_OK_BUTTON_LABEL" desc="Button text for OKing to close the browser when one or more downloads are in progress.">
         Yes, exit Chromium
       </message>
 
       <!-- Quit all apps confirmation dialog -->
       <if expr="is_macosx">
         <message name="IDS_QUIT_WITH_APPS_TITLE" desc="Title for a notification explaining that Chrome is running in the background.">
-          Chromium is running in the background.
+          Chromium is in background mode.
         </message>
       </if>
 
       <!-- Autolaunch infobar -->
       <if expr="is_win">
         <message name="IDS_AUTO_LAUNCH_INFOBAR_TEXT" desc="The text to show in the infobar when Chromium was automatically launched on startup">
           Chromium is configured to automatically launch when you start your computer.
         </message>
       </if>
 
@@ skipping 578 matching lines @@
       </if>
       <if expr="not is_android and not is_ios">
         <message name="IDS_SSL_CLOCK_ERROR" desc="Paragraph explaining that the SSL interstitial is probably caused by an incorrect clock.">
           Chromium can't establish a private connection to &lt;strong&gt;<ph name="DOMAIN">$1<ex>paypal.com</ex></ph>&lt;/strong&gt;. This is probably because your computer's date is set incorrectly (<ph name="DATE">$2<ex>Jan 1, 1970</ex></ph>). You should refresh this page after <ph name="BEGIN_LINK">&lt;a href="#" id="clock-link"&gt;</ph>you update your computer's date and time<ph name="END_LINK">&lt;/a&gt;</ph>.
         </message>
       </if>
 
     </messages>
   </release>
 </grit>