[ServiceWorker] Plumbing the request mode from the renderer to the ServiceWorker. [1/2 blink]

[1/2] blink: https://codereview.chromium.org/587213003/
[2/2] chromium: https://codereview.chromium.org/588153002/

This value is passed from the renederer to the ServiceWorker in the following steps.

In the renederer process:
  blink::ResourceRequest::setFetchRequestMode()
 blink::ResourceRequest::m_fetchRequestMode
  content::WebURLLoaderImpl::Context::Start()
   blink::WebURLRequest::fetchRequestMode()
    GetFetchRequestMode()
 conetnt::RequestInfo::service_worker_request_mode

In the browser process:
 conetnt::RequestInfo::service_worker_request_mode
  content::ResourceDispatcherHostImpl::BeginRequest()
   content::ServiceWorkerRequestHandler::InitializeHandler()
    content::ServiceWorkerProviderHost::CreateRequestHandler()
     content::ServiceWorkerControlleeRequestHandler::ServiceWorkerControlleeRequestHandler()
 content::ServiceWorkerControlleeRequestHandler::request_mode_
  content::ServiceWorkerControlleeRequestHandler::MaybeCreateJob()
   content::ServiceWorkerURLRequestJob::ServiceWorkerURLRequestJob()
 content::ServiceWorkerURLRequestJob::request_mode_
  content::ServiceWorkerURLRequestJob::CreateFetchRequest()
 content::ServiceWorkerFetchRequest::mode

In the ServiceWorker process:
 content::ServiceWorkerFetchRequest::mode
  content::ServiceWorkerScriptContext::OnFetchEvent()
   GetBlinkFetchRequestMode()
   blink::WebServiceWorkerRequest::setMode()
 blink::WebServiceWorkerRequest::WebServiceWorkerRequestPrivate::m_mode
  blink::ServiceWorkerGlobalScopeProxy::dispatchFetchEvent()
   blilnk::RespondWithObserver::create()
 blilnk::RespondWithObserver::m_requestMode

 blink::WebServiceWorkerRequest::WebServiceWorkerRequestPrivate::m_mode
  blink::Request::create()
  blink::FetchRequestData::create()
 blink::FetchRequestData::m_mode

BUG=416371,408507

Review URL: https://codereview.chromium.org/587213003

git-svn-id: svn://svn.chromium.org/blink/trunk@182885 bbb929c8-8fbe-4397-9dbb-9b2b20218538