Expose the initiating origin/URL of a navigation in the Blink public API

third_party/WebKit/Source/core/loader/DocumentLoader.cpp

Index: third_party/WebKit/Source/core/loader/DocumentLoader.cpp
diff --git a/third_party/WebKit/Source/core/loader/DocumentLoader.cpp b/third_party/WebKit/Source/core/loader/DocumentLoader.cpp
index ba90b82aa70e5e3e32e3a4f5ed2fca29cdde0e33..b759b1f245dec82097eec31bc894f3da094c9e96 100644
--- a/third_party/WebKit/Source/core/loader/DocumentLoader.cpp
+++ b/third_party/WebKit/Source/core/loader/DocumentLoader.cpp
@@ -97,9 +97,11 @@ static bool shouldInheritSecurityOriginFromOwner(const KURL& url) {
 DocumentLoader::DocumentLoader(LocalFrame* frame,
                                const ResourceRequest& req,
                                const SubstituteData& substituteData,
-                               ClientRedirectPolicy clientRedirectPolicy)
+                               ClientRedirectPolicy clientRedirectPolicy,
+                               Document* requestorDocument)
     : m_frame(frame),
       m_fetcher(FrameFetchContext::createContextAndFetcher(this, nullptr)),
+      m_requestorDocument(requestorDocument),
       m_originalRequest(req),
       m_substituteData(substituteData),
       m_request(req),
@@ -138,6 +140,7 @@ DEFINE_TRACE(DocumentLoader) {
   visitor->trace(m_fetcher);
   visitor->trace(m_mainResource);
   visitor->trace(m_writer);
+  visitor->trace(m_requestorDocument);
   visitor->trace(m_documentLoadTiming);
   visitor->trace(m_applicationCacheHost);
   visitor->trace(m_contentSecurityPolicy);
@@ -642,6 +645,9 @@ void DocumentLoader::clearMainResourceHandle() {
     return;
   m_mainResource->removeClient(this);
   m_mainResource = nullptr;
+
+  // TODO(dcheng): This doesn't really belong here.
+  m_requestorDocument = nullptr;
 }
 
 bool DocumentLoader::maybeCreateArchive() {