Improve layout and searching of History and Saved Pages.

* Add small left and right margins to the empty text so that the text
presented when there are no search results wraps more cleanly.
* Change empty message to not include search query so that the text wraps more
consistently and cleanly.
* Tweak empty messages for History and Saved Pages to be more consistent with
each other.
* Added note that the getString() method for the empty messages should
eventually be removed once all of the empty messages are translated.

Bug: 70102
Change-Id: I7adebfb1c0a06dde7f2dedd3cead8cc983d4b968