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This CL implements LocalSearchServiceProxy and
LocalSearchServiceProxyFactory. It also fixes typos and pref names.

Design doc: go/lss-sandboxing
Implementation plan: go/lss-sandboxing-impl

Bug: 1137560
Change-Id: I115a801a52fd0ed398485dd9ea9caf089fddd789
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2559477Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Jia Meng <jiameng@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Thanh Nguyen <thanhdng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832606}