Upgrade: Add 'Upgraded' header, update 'Prefer' value.

Source/core/loader/FrameFetchContext.cpp

Index: Source/core/loader/FrameFetchContext.cpp
diff --git a/Source/core/loader/FrameFetchContext.cpp b/Source/core/loader/FrameFetchContext.cpp
index 2ff4516d9dd31350df7f2432cb91f7a2a676147a..e9a2b218f9e9871cee8f40aef6d5fcd962e3af25 100644
--- a/Source/core/loader/FrameFetchContext.cpp
+++ b/Source/core/loader/FrameFetchContext.cpp
@@ -627,7 +627,7 @@ void FrameFetchContext::upgradeInsecureRequest(FetchRequest& fetchRequest)
     // Tack a 'Prefer' header to outgoing navigational requests, as described in
     // https://w3c.github.io/webappsec/specs/upgrade/#feature-detect
     if (fetchRequest.resourceRequest().frameType() != WebURLRequest::FrameTypeNone && !SecurityOrigin::isSecure(url))
-        fetchRequest.mutableResourceRequest().addHTTPHeaderField("Prefer", "return=secure-representation");
+        fetchRequest.mutableResourceRequest().addHTTPHeaderField("Prefer", "tls");
 
     if (m_document->insecureRequestsPolicy() == SecurityContext::InsecureRequestsUpgrade && url.protocolIs("http")) {
         // We always upgrade subresource requests and nested frames, we always upgrade form
@@ -645,6 +645,7 @@ void FrameFetchContext::upgradeInsecureRequest(FetchRequest& fetchRequest)
             if (url.port() == 80)
                 url.setPort(443);
             fetchRequest.mutableResourceRequest().setURL(url);
+            fetchRequest.mutableResourceRequest().addHTTPHeaderField("Upgraded", "1");
         }
     }
 }