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Enable client to customize config related to throttling - mainly
suppression duration and number of negative action count threshold
from client side API -
 std::unique_ptr<ThrottleConfig> GetThrottleConfig() {...}

This API will give client the option to override the fields related to
throttling in global config.

Internally a Delegate of ImpressionHistoryTracker will be created, and
the glue layer NotificationScheduler delegates this request.

Cleaned up throttled related parameters from schedule_params, and
impression struct and proto.

Some task need to do:
- Check consecutive negative actions instead of dismiss actions only.
- Need to write more detailed unit test to go through whole flow.
- May consider adding other way (positive impression - release throttle)
- Apply this layer to current existing clients including a more
functional web_ui for better test and play purpose.


Bug: 1053659
Change-Id: I3c767bd2be9259e74926a83ef5231ab1940b3972
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2063253
Commit-Queue: Hesen Zhang <hesen@chromium.org>
Reviewed-by: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744409}