Partially componentize //chrome/browser/search/search.{h,cc}

      Move functions from //chrome/browser/search/search.{h,cc} to the search
component //components/search/search.{h,cc} so that they can be shared
with iOS.

Move all the code in those two files (and supporting unittests) from
the &quotchrome&quot to the &quotsearch&quot namespace.

Move unittests that do not depends on non-componentized functions into
the search component.

Implements GetSearchTerms() on iOS that uses a web::WebState* instead
of content::WebContents and simplify the code to remove unsupported
features.

Directly use //components/search on iOS instead of the SearchProvider
when possible.

BUG=514239
TBR=sky,droger,benwells

Review URL: https://codereview.chromium.org/1260033003

Cr-Commit-Position: refs/heads/master@{#341525}