Revert 178571 "Teach ContentSecurityPolicy about WebURLRequest::..."

Due to bug 396582.

> Teach ContentSecurityPolicy about WebURLRequest::RequestContext.
> 
> Rather than using `Resource::Type` to make decisions about what CSP
> directive to apply to a resource request, we should be using
> WebURLRequest::RequestContext. This patch teaches ContentSecurityPolicy
> to correctly compare a URL against the right policy directive when given
> a 'ResourceContext', and pipes the value through
> 'ResourceFetcher::canRequest' to make sure its available when it needs
> to be.
> 
> BUG=390497
> 
> Review URL: https://codereview.chromium.org/398313002

TBR=mkwst@chromium.org

Review URL: https://codereview.chromium.org/418783002

git-svn-id: svn://svn.chromium.org/blink/trunk@178797 bbb929c8-8fbe-4397-9dbb-9b2b20218538