Also clean up the public interface so that it's tidier:

 - move SiteEngagementScore to its own file
 - make SiteEnagementHelper an inner class so methods can be removed from the interface

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d1c739e9e0c25c6cd8bc86d0bdaf048027a84e7a

commit d1c739e9e0c25c6cd8bc86d0bdaf048027a84e7a
Author: dominickn <dominickn@chromium.org>
Date: Thu May 12 09:24:14 2016

Migrate the site engagement service to use DidFinishNavigation.

This method will replace DidNavigateMainFrame in ths future.

BUG= 610943 

Review-Url: https://codereview.chromium.org/1967013002
Cr-Commit-Position: refs/heads/master@{#393213}

[modify] https://crrev.com/d1c739e9e0c25c6cd8bc86d0bdaf048027a84e7a/chrome/browser/engagement/site_engagement_helper.cc
[modify] https://crrev.com/d1c739e9e0c25c6cd8bc86d0bdaf048027a84e7a/chrome/browser/engagement/site_engagement_helper.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9d7502c4ce21d3441806c30817449305a0198ec7

commit 9d7502c4ce21d3441806c30817449305a0198ec7
Author: dominickn <dominickn@chromium.org>
Date: Mon May 16 07:09:16 2016

Reduce the site engagement service public interface.

This CL cleans up the site engagement service in two main ways.
SiteEngagementScore is now in its own header, implementation,
and test files, which moves nearly 1000 lines of code out of the
SiteEngagementService files. The SiteEngagementHelper is now
a public inner class of SiteEngagementService, which means
several public methods in SiteEngagementService can be made
private, cleaning up its public interface.

BUG= 610943 
TBR=tedchoc@chromium.org,avi@chromium.org,dbeam@chromium.org,peter@chromium.org,benwells@chromium.org

Review-Url: https://codereview.chromium.org/1975723002
Cr-Commit-Position: refs/heads/master@{#393800}

[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/android/preferences/important_sites_util_unittest.cc
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/banners/app_banner_settings_helper_unittest.cc
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/engagement/site_engagement_eviction_policy.cc
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/engagement/site_engagement_helper.cc
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/engagement/site_engagement_helper.h
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/engagement/site_engagement_helper_unittest.cc
[add] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/engagement/site_engagement_score.cc
[add] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/engagement/site_engagement_score.h
[add] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/engagement/site_engagement_score_unittest.cc
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/engagement/site_engagement_service.cc
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/engagement/site_engagement_service.h
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/engagement/site_engagement_service_unittest.cc
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/push_messaging/background_budget_service.cc
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/ui/tab_helpers.cc
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/browser/ui/webui/engagement/site_engagement_ui.cc
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/chrome_browser.gypi
[modify] https://crrev.com/9d7502c4ce21d3441806c30817449305a0198ec7/chrome/chrome_tests_unit.gypi

Security>UX component is deprecated in favor of the Team-Security-UX label