Add icon to the Data Saver main menu footer and update to spec

chrome/android/java/strings/android_chrome_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- android_chrome_strings.grd contains strings for Chrome for Android.
 
 FAQ:
   - How do I add, change, or remove a string?
       Just update this file.
   - Translations will happen automatically??
       Yes, indeed. Just add your string before the branch point and
       make the description good.
@@ skipping 887 matching lines @@
       </message>
       <message name="IDS_WEBSITE_SETTINGS_USB_NO_DEVICES" desc="Empty list text for a list of USB devices that sites have been granted access to.">
         No USB devices here
       </message>
 
       <!-- Data Saver -->
       <message name="IDS_DATA_REDUCTION_TITLE" desc="Menu item for Data Saver, which allows users to save mobile data by compressing network traffic.">
         Data Saver
       </message>
       <message name="IDS_DATA_REDUCTION_SAVED_LABEL" desc="Summary text for the menu item that states the amount of mobile data that was saved by Data Saver (i.e. XX MB saved). Data Saver allows users to to reduce their mobile data usage by compressing network traffic.">
-        <ph name="data">%1$s<ex>1.0 GB</ex></ph> saved since <ph name="date">%2$s<ex>3/15</ex></ph>
+        <ph name="data">%1$s<ex>1.0 GB</ex></ph> saved
+      </message>
+      <message name="IDS_DATA_REDUCTION_DATE_LABEL" desc="Summary text for the menu item that states the beginning date when the displayed mobile data was saved (i.e. XX MB saved 'since Feb 28')">
+        since <ph name="date">%1$s<ex>Feb 28</ex></ph>
       </message>
       <message name="IDS_DATA_REDUCTION_DESCRIPTION" desc="Description text for the Data Saver feature.">
         When this feature is turned on, Chrome will use Google servers to compress pages you visit before downloading them. Pages accessed using private connections (HTTPS) or in Incognito tabs will not be optimized or seen by Google.
       </message>
       <message name="IDS_DATA_REDUCTION_MENU_ITEM_SUMMARY" desc="Summary text for data reduction menu item.">
         <ph name="PERCENT">%1$s<ex>49%</ex></ph> data savings
       </message>
       <message name="IDS_DATA_REDUCTION_STATS_TITLE" desc="Data reduction statistics title.">
         Data savings
       </message>
@@ skipping 1891 matching lines @@
       </message>
       <message name="IDS_CONTEXTMENU_LINK_TITLE" desc="The title of a context menu tab when the item pressed contains more than one type. This indicates that all the actions are related to the link.">
         LINK
       </message>
       <message name="IDS_CONTEXTMENU_VIDEO_TITLE" desc="The title of a context menu tab when the item pressed contains more than one type. This indicates that all the actions are related to a video.">
         VIDEO
       </message>
     </messages>
   </release>
 </grit>