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Enable SearchEngineTabHelper to add new TemplateURL to TemplateURLService by following steps:
1. Receive messages of OSDD(Open Search Description Document) <link> in page from Js;
2. Download, parse OSDD XML file, and create TemplateURL;
3. Add TemplateURL to TemplateURLService.

The OSDD functionaliy on Js side has not been changed yet, but SearchEngineTabHelper
and SearchEngineTabHelperTest is decoupled from it. search_engine.js will
change from positive calling into message mechanism for OSDD in another CL.

Bug: 433824
Change-Id: I113e362ed1fa38cff43cea1e8fe2f591fac469c0
Reviewed-on: https://chromium-review.googlesource.com/c/1309746
Commit-Queue: Yi Su <mrsuyi@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604360}