Add client code search to docs.
Add client code search to docs.

Also, history seems to be available for internal code search.

No-Try: true
Docs-Preview: https://skia.org/?cl=171003
Change-Id: I13707664b88e3d84760f11f43d2bd7c35c2a8969
Reviewed-on: https://skia-review.googlesource.com/c/171003
Commit-Queue: Ben Wagner <3ef7217be91069877d94f7907ce5479000772cd3@google.com>
Commit-Queue: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>
Auto-Submit: Ben Wagner <3ef7217be91069877d94f7907ce5479000772cd3@google.com>
Reviewed-by: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>

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