diff -r 000000000000 -r 6474c204b198 dom/encoding/FallbackEncoding.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/encoding/FallbackEncoding.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,94 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_FallbackEncoding_h_
+#define mozilla_dom_FallbackEncoding_h_
+
+#include "nsString.h"
+
+namespace mozilla {
+namespace dom {
+
+class FallbackEncoding
+{
+public:
+
+  /**
+   * Whether FromTopLevelDomain() should be used.
+   */
+  static bool sGuessFallbackFromTopLevelDomain;
+
+  /**
+   * Gets the locale-dependent fallback encoding for legacy HTML and plain
+   * text content.
+   *
+   * @param aFallback the outparam for the fallback encoding
+   */
+  static void FromLocale(nsACString& aFallback);
+
+  /**
+   * Checks if it is appropriate to call FromTopLevelDomain() for a given TLD.
+   *
+   * @param aTLD the top-level domain (in Punycode)
+   * @return true if OK to call FromTopLevelDomain()
+   */
+  static bool IsParticipatingTopLevelDomain(const nsACString& aTLD);
+
+  /**
+   * Gets a top-level domain-depedendent fallback encoding for legacy HTML
+   * and plain text content
+   *
+   * @param aTLD the top-level domain (in Punycode)
+   * @param aFallback the outparam for the fallback encoding
+   */
+  static void FromTopLevelDomain(const nsACString& aTLD, nsACString& aFallback);
+
+  // public API ends here!
+
+  /**
+   * Allocate sInstance used by FromLocale().
+   * To be called from nsLayoutStatics only.
+   */
+  static void Initialize();
+
+  /**
+   * Delete sInstance used by FromLocale().
+   * To be called from nsLayoutStatics only.
+   */
+  static void Shutdown();
+
+private:
+
+  /**
+   * The fallback cache.
+   */
+  static FallbackEncoding* sInstance;
+
+  FallbackEncoding();
+  ~FallbackEncoding();
+
+  /**
+   * Invalidates the cache.
+   */
+  void Invalidate()
+  {
+    mFallback.Truncate();
+  }
+
+  static void PrefChanged(const char*, void*);
+
+  /**
+   * Gets the fallback encoding label.
+   * @param aFallback the fallback encoding
+   */
+  void Get(nsACString& aFallback);
+
+  nsCString mFallback;
+};
+
+} // dom
+} // mozilla
+
+#endif // mozilla_dom_FallbackEncoding_h_
+