message: Prepare CHANGELOG for 4.0.0-pre.2 release.
diff: @@ -5,10 +5,12 @@ All notable changes to this project will be documented in this file.
  The format is based on [Keep a Changelog](http://keepachangelog.com/)
  and this project adheres to [Semantic Versioning](http://semver.org/).
  -## Unreleased
  +<!-- ## Unreleased -->
  +<!-- Add new, unreleased changes here. -->
  +
  +## 4.0.0-pre.2 - 2018-03-20
  - Upgraded to use `polymer-analyzer` version `3.0.0-pre.17`.
  - Switched to `FsUrlResolver` from `PackageUrlResolver` as the default `UrlResolver` for bundling contexts. This is because `PackageUrlResolver` is intended for component analysis, not application analysis.
  -<!-- Add new, unreleased changes here. -->
  ## 4.0.0-pre.1 - 2018-03-07
  - [BREAKING] Upgraded to use `polymer-analyzer` version `3.0.0-pre.13` which requires the `ResolvedUrl` type in nearly all places where URLs are exchanged and provides strict typing on URLs used globally. Eliminated the local `UrlString` type.
  