Change StyleResolver::document() to be private

Source/core/css/resolver/StyleResolver.h

Index: Source/core/css/resolver/StyleResolver.h
diff --git a/Source/core/css/resolver/StyleResolver.h b/Source/core/css/resolver/StyleResolver.h
index 63c620b6234fd2fa8c2c7abc8054489329d7d4bc..d0dffc8ecef5283cda0042651a0fa572bce5579a 100644
--- a/Source/core/css/resolver/StyleResolver.h
+++ b/Source/core/css/resolver/StyleResolver.h
@@ -1,3 +1,4 @@
+
 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
@@ -118,10 +119,6 @@ public:
 
     static PassRefPtr<RenderStyle> styleForDocument(Document&);
 
-    // FIXME: This only has 5 callers and should be removed. Callers should be explicit about
-    // their dependency on Document* instead of grabbing one through StyleResolver.
-    Document& document() { return *m_document; }
-
     // FIXME: It could be better to call appendAuthorStyleSheets() directly after we factor StyleResolver further.
     // https://bugs.webkit.org/show_bug.cgi?id=108890
     void appendAuthorStyleSheets(const WillBeHeapVector<RefPtrWillBeMember<CSSStyleSheet> >&);