Revert 154452 "Refactoring: Introduce ResouceLoaderHost interfac..."

> Refactoring: Introduce ResouceLoaderHost interface for unloading ResourceLoader.
> 
> This moves several direct dependencies of ResourceLoader into
> newly inroduced ResouceLoaderHost interface, which is implemented by
> CachedResourceLoader.
> 
> The motivation here is to make ResourceLoader working without DocumentLoader
> and FrameLoader so that scripts can be loaded through imported documents, which
> doesn't have a DocumentLoader.
> 
> Note that CachedResourceLoader already lives without DocumentLoader in some case,
> thus it is natural to localize such kind of complication there and keep ResourceLoader
> straightforward.
> 
> BUG=240592
> TEST=none
> R=japhet@chromium.org
> 
> Review URL: https://codereview.chromium.org/19574002

TBR=morrita@chromium.org

Review URL: https://codereview.chromium.org/19683007

git-svn-id: svn://svn.chromium.org/blink/trunk@154458 bbb929c8-8fbe-4397-9dbb-9b2b20218538