Revert of Ancestors count towards first-partyness.

Revert of Ancestors count towards first-partyness. (patchset #3 id:40001 of https://codereview.chromium.org/1075163002/)

Reason for revert:
This apparently produces behavior that diverges from Firefox. Reverting as I'm OOO, and can't really investigate until next week.

BUG=482812
Original issue's description:
> Ancestors count towards first-partyness.
> 
> We currently set requests' "firstPartyForCookies" property based on the
> top-level document's URL. We ought to harden this property to account
> for good.com -> evil.com -> good.com ancestor chains.
> 
> The top-level 'good.com' should be considered a first-party context.
> The nested 'good.com' should not.
> 
> This CL adds this behavior behind a runtime flag. If the intent to ship
> at [1] is approved, I'll remove the flag in a followup CL.
> 
> [1]: https://groups.google.com/a/chromium.org/d/msg/blink-dev/ZvMEJMSU6po/wKWAfpIe6vUJ
> 
> BUG=459154
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=193884

TBR=jochen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=459154

[Mike West, 2015-05-05 16:18:27]

Created Revert of Ancestors count towards first-partyness.

[commit-bot: I haz the power, 2015-05-05 16:18:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1118373007/1

[commit-bot: I haz the power, 2015-05-05 16:19:54]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-05-05 16:19:56]

Failed to apply patch for Source/core/dom/Document.cpp:
While running patch -p1 --forward --force --no-backup-if-mismatch;
  patching file Source/core/dom/Document.cpp
  Hunk #1 FAILED at 3979.
  1 out of 1 hunk FAILED -- saving rejects to file
Source/core/dom/Document.cpp.rej

Patch:       Source/core/dom/Document.cpp
Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index
93ad71a9ecf2d93b25e0ce23347ba706648866b5..fef902a5f5c3d5c032a78b4292bf89db04a492d9
100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -3979,26 +3979,6 @@
 
 const KURL& Document::firstPartyForCookies() const
 {
-    if (!RuntimeEnabledFeatures::firstPartyIncludesAncestorsEnabled())
-        return topDocument().url();
-
-    // We're intentionally using the URL of each document rather than the
document's SecurityOrigin.
-    // Sandboxing a document into a unique origin shouldn't effect
first-/third-party status for
-    // cookies and site data.
-    RefPtr<SecurityOrigin> topOrigin =
SecurityOrigin::create(topDocument().url());
-    const Document* currentDocument = this;
-    while (currentDocument) {
-        // Skip over srcdoc documents, as they are always same-origin with
their closest non-srcdoc parent.
-        while (currentDocument->isSrcdocDocument())
-            currentDocument = currentDocument->parentDocument();
-        ASSERT(currentDocument);
-
-        if (!topOrigin->canRequest(currentDocument->url()))
-            return SecurityOrigin::urlWithUniqueSecurityOrigin();
-
-        currentDocument = currentDocument->parentDocument();
-    }
-
     return topDocument().url();
 }

[commit-bot: I haz the power, 2015-05-05 16:20:23]

The CQ bit was unchecked by commit-bot@chromium.org