Rename CachedResource to Resouce, and related classes respectively.

This change contains following renames:
- CachedResoue -> Resource
- CachedResourceHandle -> ResourcePtr
  (dropped "Handle" to avoid confusion with other handle classes)
- CachedResourceInitiatorInfo -> FetchInitiatorInfo
- CachedResourceClient -> ResourceClient
- CachedResourceClient -> ResourceClientWalker

TEST=none
BUG=none
TBR=abarth, japhet@chromium.org

Review URL: https://chromiumcodereview.appspot.com/20215004

git-svn-id: svn://svn.chromium.org/blink/trunk@154984 bbb929c8-8fbe-4397-9dbb-9b2b20218538