Loader rename continues.

This round renames part of Resource subclasses.

- CachedDocument -> DocumentResource
- CachedSVGDocumentReference -> DocumentResourceReference
- CachedShader -> ShaderResource
- CachedTextTrack -> TextTrackResource
- CachedXSLStyleSheet -> XSLStyleSheetResouce
- CachedFont -> FontResource
- StyleCachedShader -> StyleFetchedShader

R=abarth,japhet
BUG=263277
TEST=none

Review URL: https://chromiumcodereview.appspot.com/22546002

git-svn-id: svn://svn.chromium.org/blink/trunk@155758 bbb929c8-8fbe-4397-9dbb-9b2b20218538