Commit empty document instead of canceling the load for blocked CSP/XFO responses.

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

Index: third_party/WebKit/Source/core/dom/DocumentInit.cpp
diff --git a/third_party/WebKit/Source/core/dom/DocumentInit.cpp b/third_party/WebKit/Source/core/dom/DocumentInit.cpp
index c75e302fb53fa52ee48faf6f25fb67338b1af2fe..fe487a8f66f5a2e5adb8b4aaab04eb8fa991896b 100644
--- a/third_party/WebKit/Source/core/dom/DocumentInit.cpp
+++ b/third_party/WebKit/Source/core/dom/DocumentInit.cpp
@@ -104,7 +104,18 @@ LocalFrame* DocumentInit::frameForSecurityContext() const
 SandboxFlags DocumentInit::getSandboxFlags() const
 {
     ASSERT(frameForSecurityContext());
-    return frameForSecurityContext()->loader().effectiveSandboxFlags();
+    FrameLoader* loader = &frameForSecurityContext()->loader();
+    SandboxFlags flags = loader->effectiveSandboxFlags();
+
+    // If the load was blocked by X-Frame-Options or CSP, force the Document's
+    // origin to be unique, so that the blocked document appears to be a normal
+    // cross-origin document's load per CSP spec:
+    // https://www.w3.org/TR/CSP2/#directive-frame-ancestors
+    DocumentLoader* documentLoader = loader->provisionalDocumentLoader() ? loader->provisionalDocumentLoader() : loader->documentLoader();

[Nate Chapin, 2016/03/01 20:26:11]

Is it really possible for this to be either document loader? I would have
thought it's always one or the other.

[alexmos, 2016/03/02 01:30:55]

Good point.  Looking closer I think this should just use documentLoader(). 
(This is called after FrameLoader::prepareForCommit, which releases the
provisional one.)  I've changed it and things still work.

That said, I based this off of DocumentInit::isHostedInReservedIPRange(), which
has this check and is also used solely in Document::initSecurityContext.  Mike,
you added it in https://codereview.chromium.org/845303003 - was there a reason
for checking both loaders?  

+    if (documentLoader && documentLoader->wasBlockedAfterXFrameOptionsOrCSP())
+        flags |= SandboxOrigin;
+
+    return flags;
 }
 
 bool DocumentInit::shouldEnforceStrictMixedContentChecking() const