Mostly done, should land today or tomorrow.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8048f8d8d5153a0e530529e883c78582853d0b15

commit 8048f8d8d5153a0e530529e883c78582853d0b15
Author: jkrcal <jkrcal@chromium.org>
Date: Wed Sep 21 10:25:24 2016

Extending the UserClassifier to actually support classification.

This CL adds actual classification to the UserClassifier.
So far, only simple classification thresholds are implemented.

The CL also includes a new snippets-internals section and a bit of
refactoring.

In a follow-up CLs, all the parameters will become configurable by
variations.

BUG= 648252 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2346263002
Cr-Commit-Position: refs/heads/master@{#420022}

[modify] https://crrev.com/8048f8d8d5153a0e530529e883c78582853d0b15/chrome/browser/android/ntp/ntp_snippets_bridge.cc
[modify] https://crrev.com/8048f8d8d5153a0e530529e883c78582853d0b15/chrome/browser/resources/snippets_internals.html
[modify] https://crrev.com/8048f8d8d5153a0e530529e883c78582853d0b15/chrome/browser/resources/snippets_internals.js
[modify] https://crrev.com/8048f8d8d5153a0e530529e883c78582853d0b15/chrome/browser/ui/webui/snippets_internals_message_handler.cc
[modify] https://crrev.com/8048f8d8d5153a0e530529e883c78582853d0b15/chrome/browser/ui/webui/snippets_internals_message_handler.h
[modify] https://crrev.com/8048f8d8d5153a0e530529e883c78582853d0b15/components/ntp_snippets/user_classifier.cc
[modify] https://crrev.com/8048f8d8d5153a0e530529e883c78582853d0b15/components/ntp_snippets/user_classifier.h