Update New Tab Bubble Promo String.

Update the New Tab Bubble Promo String to "Add tabs and switch between
pages".

Bug: 779656
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Ia42386ecc45e45ccf93105d48ff5bdd898cf4058
Reviewed-on: https://chromium-review.googlesource.com/809844Reviewed-by: edchin <edchin@chromium.org>
Commit-Queue: Gregory Chatzinoff <gchatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521860}

ios/chrome/app/strings/ios_strings.grd

@@ -708,8 +708,8 @@ locale.  The strings in this file are specific to iOS.
       <message name="IDS_IOS_NEW_TAB_INCOGNITO" desc="Title for the Incognito panel of the new tab page.">
         Incognito
       </message>
-      <message name="IDS_IOS_NEW_TAB_IPH_PROMOTION_TEXT" desc="Text for the New Tab Tip in-product help promotion, explaining that new tabs can be opened. [iOS only]" meaning="The user has never created a new tab, and a bubble is displayed pointing to the tab switcher to inform users how to create tabs.">
-        Create multiple tabs for all your tasks
+      <message name="IDS_IOS_NEW_TAB_IPH_PROMOTION_TEXT" desc="Text for the New Tab Tip in-product help promotion, explaining that new tabs can be added and switched between. [iOS only]" meaning="The user has never created a new tab, and a bubble is displayed pointing to the tab switcher to inform users how to create tabs and switch between them.">
+        Add tabs and switch between pages
       </message>
       <message name="IDS_IOS_NEW_TAB_LEARN_MORE_ABOUT_SUGGESTED_CONTENT" desc="Text in the footer of the New Tab Page. Part of the text is a link to a help center page where the user can learn more about suggested content.">
         <ph name="BEGIN_LINK">BEGIN_LINK</ph>Learn more<ph name="END_LINK">END_LINK</ph> about suggested content