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Adds support for persisting and later reporting user interaction
to the server in support of the offline sanitized click-log.

BACKGROUND:
This change allows the server to log outcomes from interactions and associate
them with the privacy-safe documents in the Search Index. See go/cs-sanitized
for more details on this design.

DESIGN OVERVIEW:
When the server recognizes a document it generates a random EventID and logs
it to sawmill and returns it to the client in the response to the Resolve
request.  The client passes the EventID up to Java and persists it in local
device storage along with the user-interaction outcomes.  The next time
the user makes a Resolve request the client checks for previous data, and if
present it sends it as part of the Context to the server (and erases it
from storage).

DETAILS:
This CL introduces a new interface ContextualSearchInteractionPersister to
persist user interactions, and an implementation that uses local storage.

The manager detects a new parameter for the EventID returned in the
Resolve request. It stores this and an encoded set of bits that describe
the user-interaction for that event in local storage.
Any subsequent Resolve request checks for a previous EventID and when
non-zero sends it along with the user-interaction results in CGI params
to the server.  Support for these params on the client and server have
already landed.

If the server never sends an Event ID to log, then the client won't
change it's behavior.  The server does not yet send these Event IDs.

BUG=872902

Change-Id: Ief9a95625b16a4b0a3be5325ed1adadff9c791b9
Reviewed-on: https://chromium-review.googlesource.com/c/1170352
Commit-Queue: Donn Denman <donnd@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622993}