Add iOS strings for contextual search in chrome://flags.

ios/chrome/app/strings/ios_strings.grd

Index: ios/chrome/app/strings/ios_strings.grd
diff --git a/ios/chrome/app/strings/ios_strings.grd b/ios/chrome/app/strings/ios_strings.grd
index 5136dac6bc9130e6ffee578da7c0611d2015edb3..5f77d57730cf80eb79da5d1831b6d9b05dc1fa40 100644
--- a/ios/chrome/app/strings/ios_strings.grd
+++ b/ios/chrome/app/strings/ios_strings.grd
@@ -175,6 +175,13 @@ all other OS specific variables will be false.
         Not Now
       </message>
 
+      <message name="IDS_IOS_FLAGS_CONTEXTUAL_SEARCH" desc="Title for the flag to enable Contextual Search.">
+        Contextual Search
+      </message>
+      <message name="IDS_IOS_FLAGS_CONTEXTUAL_SEARCH_DESCRIPTION" desc="Description for the flag to enable Contextual Search.">
+        Whether or not Contextual Search is enabled.
+      </message>
+
       <!-- iOS Net-Export strings -->
       <message name="IDS_IOS_NET_EXPORT_NO_EMAIL_ACCOUNTS_ALERT_MESSAGE" desc="The message of the alert informing a user with no email accounts that he or she needs to configure an email account to send net-export data. [Length: 70em]">
         To send net-export data, please configure your email account in the Settings app.