Allow lax MIME type parsing for same-origin CSS in quirks mode.

Source/core/fetch/CSSStyleSheetResource.h

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller <mueller@kde.org>
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
     version 2 of the License, or (at your option) any later version.
@@ skipping 20 matching lines @@
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class CSSParserContext;
 class ResourceClient;
 class StyleSheetContents;
 
 class CSSStyleSheetResource final : public StyleSheetResource {
 public:
+    enum class MIMETypeCheck { Strict, Lax };
+
     CSSStyleSheetResource(const ResourceRequest&, const String& charset);
     virtual ~CSSStyleSheetResource();
     DECLARE_VIRTUAL_TRACE();
 
-    const String sheetText(bool* hasValidMIMEType = 0) const;
+    const String sheetText(MIMETypeCheck = MIMETypeCheck::Strict) const;
 
     const AtomicString mimeType() const;
 
     virtual void didAddClient(ResourceClient*) override;
 
     PassRefPtrWillBeRawPtr<StyleSheetContents> restoreParsedStyleSheet(const CSSParserContext&);
     void saveParsedStyleSheet(PassRefPtrWillBeRawPtr<StyleSheetContents>);
 
 protected:
     virtual bool isSafeToUnlock() const override;
     virtual void destroyDecodedDataIfPossible() override;
 
 private:
-    bool canUseSheet(bool* hasValidMIMEType) const;
+    bool canUseSheet(MIMETypeCheck) const;
     virtual void dispose() override;
     virtual void checkNotify() override;
 
     String m_decodedSheetText;
 
     RefPtrWillBeMember<StyleSheetContents> m_parsedStyleSheetCache;
 };
 
 DEFINE_RESOURCE_TYPE_CASTS(CSSStyleSheet);
 
 }
 
 #endif