[AiS] Add prefetch query parameters

Answers needs to signal to search if there is a reasonable guess at the
full query text. For this purpose, it will set pfq= to the full query
text and qha= to the answers type.

This change enables setting those parameters via TemplateUrl.

BUG=370192
[email protected]

Review URL: https://codereview.chromium.org/342133002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@279221 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed