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

chrome/android/java/strings/android_chrome_strings.grd

Index: chrome/android/java/strings/android_chrome_strings.grd
diff --git a/chrome/android/java/strings/android_chrome_strings.grd b/chrome/android/java/strings/android_chrome_strings.grd
index 4f40eca636df1717f8ededd9362ff124e6c2355b..39fb94b9fb7541b0ea0a2cdd0e858b131c1dd3cb 100644
--- a/chrome/android/java/strings/android_chrome_strings.grd
+++ b/chrome/android/java/strings/android_chrome_strings.grd
@@ -905,7 +905,10 @@ To obtain new licenses, connect to the internet and play your downloaded content
         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.