Add context menu when long press on a reading list entry

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 79abf33717dc010c54bafe0a1adaa45f4fbd7f17..b8e7ae149c35495c8e99966096718466ecc1ee7b 100644
--- a/ios/chrome/app/strings/ios_strings.grd
+++ b/ios/chrome/app/strings/ios_strings.grd
@@ -1071,6 +1071,9 @@ Handoff must also be enabled in the General section of Settings, and your device
       <message name="IDS_IOS_READING_LIST_CANCEL_BUTTON" desc="Label of the button to stop editing the reading list entries (delete, mark as read/unread) [Length: 25em]" meaning="Stop editing. [Length: 25em]">
         Cancel
       </message>
+      <message name="IDS_IOS_READING_LIST_CONTENT_CONTEXT_OFFLINE" desc="Title of the button to display the Offline version instead of the Online one.">
+        View Offline Version

[stkhapugin, 2017/01/30 10:34:53]

Please add a length in em

[gambard, 2017/01/31 09:35:40]

Done.

+      </message>
       <message name="IDS_IOS_READING_LIST_DELETE_ALL_READ_BUTTON" desc="Label of the button to delete all the reading list entries read [Length: 25em]" meaning="Delete all the read entries. [Length: 25em]">
         Delete Read
       </message>