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This simplifies the code some by eliminating google_profile_helper entirely, and
ensures that everyone who is trying to construct a "search URL" will correctly
respect things like the command-line Google base URL override switch.

This also moves some related code from URLRequestMockHTTPJob into its lone
caller and stops assuming that the search URL scheme is always HTTP.

BUG=364183
TEST=none

Review URL: https://codereview.chromium.org/896943002

Cr-Commit-Position: refs/heads/master@{#314600}