Allow add to homescreen and app banner strings to be changed via variations.

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 2339c426250c897f9cb5c227c8dc4195294c113d..997f8234e6957f549d1ea60b884ac3f454a33f6f 100644
--- a/chrome/android/java/strings/android_chrome_strings.grd
+++ b/chrome/android/java/strings/android_chrome_strings.grd
@@ -1558,9 +1558,21 @@ To obtain new licenses, connect to the internet and play your downloaded content
       </message>
 
       <!-- Add to Home screen strings -->
-      <message name="IDS_MENU_ADD_TO_HOMESCREEN" desc="Menu item for adding a shortcut to the Home screen. [CHAR-LIMIT=27]">
+      <message name="IDS_MENU_ADD_TO_HOMESCREEN" desc="Menu item for adding a shortcut to the Home screen (default title). [CHAR-LIMIT=27]">
         Add to Home screen
       </message>
+      <message name="IDS_MENU_ADD_TO_HOMESCREEN_ADD" desc="Menu item for adding a shortcut to the Home screen. [CHAR-LIMIT=27]">
+        Add shortcut
+      </message>
+      <message name="IDS_MENU_ADD_TO_HOMESCREEN_INSTALL" desc="Menu item for adding a shortcut to the Home screen. [CHAR-LIMIT=27]">
+        Install web app
+      </message>
+      <message name="IDS_APP_BANNER_ADD" desc="A button in an app banner to confirm adding a site to homescreen">
+        Add
+      </message>
+      <message name="IDS_APP_BANNER_INSTALL" desc="A button in an app banner to confirm adding a site to homescreen">
+        Install
+      </message>
       <message name="IDS_ADDED_TO_HOMESCREEN" desc="Indicates that the website with the specified name was added to the user's Home screen.">
         <ph name="NAME">%1$s<ex>Google</ex></ph> was added to your Home screen
       </message>