MD Settings: Add link around "omnibox" text in search section.

chrome/app/settings_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Settings-specific strings (included from generated_resources.grd). -->
 <grit-part>
   <!-- About Page -->
   <message name="IDS_SETTINGS_ABOUT_PAGE_BROWSER_VERSION" desc="The text label describing the version of the browser, example: Version 57.0.2937.0 (Developer Build) unknown (64-bit)">
     Version <ph name="PRODUCT_VERSION">$1<ex>15.0.865.0</ex></ph> (<ph name="PRODUCT_CHANNEL">$2<ex>Developer Build</ex></ph>) <ph name="PRODUCT_MODIFIER">$3</ph> <ph name="PRODUCT_VERSION_BITS">$4</ph>
   </message>
   <if expr="chromeos">
     <message name="IDS_SETTINGS_ABOUT_PAGE_DETAILED_BUILD_INFO" desc="Label describing the section that shows detailed information about the current Chrome build.">
       Detailed build information
@@ skipping 1596 matching lines @@
   </message>
   <message name="IDS_SETTINGS_RESET_VIEW_REPORTED_SETTINGS" desc="Label of a link that when clicked displays the settings that will be reported to Google for analysis.">
     View report settings
   </message>
 
   <!-- Search Page -->
   <message name="IDS_SETTINGS_SEARCH" desc="Name of the settings page which displays search engine preferences.">
     Search engine
   </message>
   <message name="IDS_SETTINGS_SEARCH_EXPLANATION" desc="Explanation for the search engine dropdown setting.">
-    Search engine used when searching from the omnibox
+    Search engine used when searching from the <ph name="BEGIN_LINK">&lt;a target="_blank" href="$1"&gt;</ph>omnibox<ph name="END_LINK">&lt;/a&gt;</ph>
   </message>
   <message name="IDS_SETTINGS_SEARCH_MANAGE_SEARCH_ENGINES" desc="Label for the Manage Search Engines button.">
     Manage search engines
   </message>
   <message name="IDS_SETTINGS_SEARCH_MANAGE_SEARCH_ENGINES_DESCRIPTION" desc="Description label for the Manage Search Engines button.">
     Add, edit, or remove search engines
   </message>
   <message name="IDS_SETTINGS_SEARCH_OK_GOOGLE_LABEL" desc="Label for the checkbox which enables the OK Google hotword.">
     Enable "Ok Google" to start a voice search.
   </message>
@@ skipping 1225 matching lines @@
       System
     </message>
     <message name="IDS_SETTINGS_SYSTEM_HARDWARE_ACCELERATION_LABEL" desc="Label for the checkbox that forces Chrome to render via hardware acceleration (GPU) when available.">
       Use hardware acceleration when available
     </message>
     <message name="IDS_SETTINGS_SYSTEM_PROXY_SETTINGS_BUTTON" desc="Text for the button that changes a user's network proxy settings.">
       Change proxy settings
     </message>
   </if>
 </grit-part>