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Refactors the Contextual Search Component to use the layered directory
layout recommended for iOS support.  This CL splits the top-level
directories into /core and /content.  A few files that are clearly
not dependent on any content have been moved to /core/, and everything
else is moved to /content/.  There will be some additional /core/ files
landing soon.

This CL doesn't change any logic or functionality, it just moves source
files.

BUG=646019,825428

Change-Id: Ia4bf5cdecaabf7d9515b2d4fca855db29b1c4b1c
Reviewed-on: https://chromium-review.googlesource.com/1173019Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Donn Denman <donnd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584566}