chrome/blink: Add functionality for in-product help for media elements.

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 3057 matching lines @@
       </message>
       <message name="IDS_IPH_DATA_SAVER_PREVIEW_TEXT" desc="In-product help for when a data saver preview page and infobar are shown.">
           Chrome is using less data to show you this page
       </message>
       <message name="IDS_IPH_DATA_SAVER_DETAIL_TEXT" desc="The in-product-help message to open data saver.">
         See how much data you've saved
       </message>
       <message name="IDS_IPH_DATA_SAVER_DETAIL_ACCESSIBILITY_TEXT" desc="The in-product-help accessibility text to open data saver.">
         See how much data you've saved from the More Options button
       </message>
-
+      <message name="IDS_IPH_MEDIA_DOWNLOAD_TEXT" desc="The in-product-help message to download a video.">
+        Download videos to watch later
+      </message>
+      <message name="IDS_IPH_MEDIA_DOWNLOAD_ACCESSIBILITY_TEXT" desc="The in-product-help accessibility text to download a video.">
+        Download videos to watch later using the Download button

[mlamouri (slow - plz ping), 2017/07/13 21:14:27]

Are you showing this only for videos?

[Khushal, 2017/07/17 17:52:20]

Yes. I added an if check for video element in MayBeDispatchInProductHelpTrigger.

+      </message>
       <!-- Search Widget strings -->
       <message name="IDS_SEARCH_WIDGET_DEFAULT" desc="Default text for the search widget">
         Search
       </message>
       <message name="IDS_SEARCH_WITH_PRODUCT" desc="Text for search widget with a search engine name">
         Search with <ph name="PRODUCT_NAME">%1$s<ex>Google</ex></ph>
       </message>
 
       <!-- Launcher Shortcuts -->
       <message name="IDS_DISABLED_INCOGNITO_LAUNCHER_SHORTCUT_MESSAGE" desc="Text for a toast displayed prompting the user to remove the disabled 'New incognito tab' app shortcut and recreate it.">
@@ skipping 30 matching lines @@
       </message>
       <message name="IDS_BOTTOM_SHEET_HISTORY_TAB" desc="Accessibility string read when the history tab is selected.">
         History tab selected
       </message>
       <message name="IDS_BOTTOM_SHEET_HOME_TAB" desc="Accessibility string read when the home tab is selected.">
         Home tab selected
       </message>
     </messages>
   </release>
 </grit>