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Updated and refactored URLIndexPrivateData::HistoryItemsForTerms to handle searching the history for both the original search string as well as the string with a break inserted.

The goal is to support mid-word autocomplete in the Omnibox.  Currently, if the user types "funtimes", inserts the cursor between the "n" and the "t" and begins typing the word "good" the Ominbox will search for URL results that match "fungood times" only.  We want to also search for "fungoodtimes".

BUG=591979
TEST=0. Clear browser history.
1. Visit the following link: https://twitter.com/fungoodtimes
2. Open a new browser tab.
3.Type into the Omnibox "funtimes".  Note the lack of the suggestion for the above URL.
4. Insert the cursor between the "n" and "t" in "funtime" and type "good".
5. The above URL should show in the autocomplete list.

Review-Url: https://codereview.chromium.org/2364553004
Cr-Commit-Position: refs/heads/master@{#420721}