Rename NavigationInitiationType::USER_INITIATED to BROWSER_INITIATED.

Every navigation can be initiated by Browser or Renderer.

Browser-initiated navigations are:
 - url was typed into omnibox
 - back/forward/reload was tapped
Renderer-initiated navigations are:
 - link was clicked
 - state was replaced


Every navigation may or may not have user gesture.

Navigations with user gesture:
  - all browser-initiated navigations
  - link was clicked
  - pushState was called in response to user gesture
Navigations without user gesture:
  - pushState was called without user gesture (web site did that)
  - other client redirects which initiated by a web site

To avoid confusion between all these terms USER_INITIATED is renamed to
BROWSER_INITIATED, which matches //content terminology used in
WebContentsObserver comments.


Bug: None
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I9b33145da0cf3a670fff312d913c9b5cc0cb9dd3
Reviewed-on: https://chromium-review.googlesource.com/1062217
Reviewed-by: Danyao Wang <danyao@chromium.org>
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#559567}
12 files changed