More loader class renaming.

- CachedScript -> ScriptResource
- CachedImage -> ImageResource
- CachedRawResource -> RawResource
- CachedCSSStyleSheet -> CSSStyleSheetResource

R=abarth,japhet
BUG=263277
TEST=none

Review URL: https://chromiumcodereview.appspot.com/22362008

git-svn-id: svn://svn.chromium.org/blink/trunk@155856 bbb929c8-8fbe-4397-9dbb-9b2b20218538