SameSite: Correctly set requests' initiator for new tabs.

third_party/WebKit/Source/core/dom/Document.cpp

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index 0e123a4bd445c26378da5f43e2689b6c21d2a9c0..bdd056da6d6cbb39633ff0630c5647f4d03abdf8 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -4159,6 +4159,10 @@ String Document::lastModified() const
 
 const KURL Document::firstPartyForCookies() const
 {
+    // If this is an imported document, grab its master document's first-party:
+    if (importsController() && importsController()->master() && importsController()->master() != this)
+        return importsController()->master()->firstPartyForCookies();

[Mike West, 2016/06/21 09:01:01]

Note also: I could split this and the 'render_frame_impl.cc'
'firstPartyForCookies()' piece out into a separate patch if you like. The one
requires the other, as the current implementation is busted for imports (they
have no `frame()`, so asking them for a first-party causes a null-deref.

+
     // TODO(mkwst): This doesn't correctly handle sandboxed documents; we want to look at their URL,
     // but we can't because we don't know what it is.
     Frame* top = frame()->tree().top();