GitLab

This commit:
- breaks the inheritance relationship of ChromeSearchResult and SearchResult;
- removes all SearchModel class references from Chrome;
- removes ChromeSearchResult::Duplicate and uses SearchResultMetadata to
  publish results.

Bug: 733662
Change-Id: Iacf407818d74a69daa06c6649cfbf255b8921df4
Reviewed-on: https://chromium-review.googlesource.com/1038766Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Jiaquan He <hejq@google.com>
Cr-Commit-Position: refs/heads/master@{#556690}