Use default url to inform app of prov40 stages

[ Merge of http://go/wvgerrit/147457 ]

For the first stage of provisioning 4, the default url is appended with
"&preProvisioning=true" as an indicator to the app that the current
stage is the first stage.

Design doc:https://docs.google.com/document/d/1NZVKCsBtaMJdTjj2C9FzW8s-s4eEj2niu5SPlw7EvRM/edit

Bug: 224375138
Test: GtsMediaTestCase on sunfish
Change-Id: I49ba6f799b51b042461a32c51e4e20c6071227b8

libwvdrmengine/cdm/core/include/certificate_provisioning.h

@@ -82,7 +82,8 @@ class CertificateProvisioning {
       const std::string& origin, const std::string& spoid,
       CdmProvisioningRequest* request, std::string* default_url);
   CdmResponseType GetProvisioning40RequestInternal(
-      wvutil::FileSystem* file_system, CdmProvisioningRequest* request);
+      wvutil::FileSystem* file_system, CdmProvisioningRequest* request,
+      std::string* default_url);
   CdmResponseType FillEncryptedClientId(
       const std::string& client_token,
       video_widevine::ProvisioningRequest& provisioning_request);