Add HttpProtocolHandler and convert everything to use it

net/url_request/url_request_test_util.h

Index: net/url_request/url_request_test_util.h
diff --git a/net/url_request/url_request_test_util.h b/net/url_request/url_request_test_util.h
index a18ef8ce1303a8bfc11779a9e95f59f0139cad2e..1c5b4784a389636bb6c6e48d27ef0494c0fd0f46 100644
--- a/net/url_request/url_request_test_util.h
+++ b/net/url_request/url_request_test_util.h
@@ -38,6 +38,7 @@
 #include "net/http/http_request_headers.h"
 #include "net/proxy/proxy_service.h"
 #include "net/ssl/ssl_config_service_defaults.h"
+#include "net/url_request/http_protocol_handler.h"
 #include "net/url_request/url_request.h"
 #include "net/url_request/url_request_context.h"
 #include "net/url_request/url_request_context_getter.h"
@@ -409,7 +410,9 @@ class TestNetworkDelegate : public NetworkDelegateImpl {
 
 //-----------------------------------------------------------------------------
 
-// A simple ProtocolHandler that returns a pre-built URLRequestJob only once.
+// A simple ProtocolHandler that returns a pre-built URLRequestJob only once,
+// and falls back to a normal HttpProtocolHandler implementation if no pre-built
+// URLRequestJob is present.
 class TestJobInterceptor : public URLRequestJobFactory::ProtocolHandler {
  public:
   TestJobInterceptor();
@@ -421,6 +424,7 @@ class TestJobInterceptor : public URLRequestJobFactory::ProtocolHandler {
   void set_main_intercept_job(std::unique_ptr<URLRequestJob> job);
 
  private:
+  std::unique_ptr<HttpProtocolHandler> http_protocol_handler_;
   mutable std::unique_ptr<URLRequestJob> main_intercept_job_;
 };