diff -r 000000000000 -r 6474c204b198 dom/encoding/FallbackEncoding.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/encoding/FallbackEncoding.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,168 @@
+/* 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/. */
+
+#include "mozilla/dom/FallbackEncoding.h"
+
+#include "mozilla/dom/EncodingUtils.h"
+#include "nsUConvPropertySearch.h"
+#include "nsIChromeRegistry.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Services.h"
+
+namespace mozilla {
+namespace dom {
+
+static const char* localesFallbacks[][3] = {
+#include "localesfallbacks.properties.h"
+};
+
+static const char* domainsFallbacks[][3] = {
+#include "domainsfallbacks.properties.h"
+};
+
+static const char* nonParticipatingDomains[][3] = {
+#include "nonparticipatingdomains.properties.h"
+};
+
+FallbackEncoding* FallbackEncoding::sInstance = nullptr;
+bool FallbackEncoding::sGuessFallbackFromTopLevelDomain = true;
+
+FallbackEncoding::FallbackEncoding()
+{
+  MOZ_COUNT_CTOR(FallbackEncoding);
+  MOZ_ASSERT(!FallbackEncoding::sInstance,
+             "Singleton already exists.");
+}
+
+FallbackEncoding::~FallbackEncoding()
+{
+  MOZ_COUNT_DTOR(FallbackEncoding);
+}
+
+void
+FallbackEncoding::Get(nsACString& aFallback)
+{
+  if (!mFallback.IsEmpty()) {
+    aFallback = mFallback;
+    return;
+  }
+
+  const nsAdoptingCString& override =
+    Preferences::GetCString("intl.charset.fallback.override");
+  // Don't let the user break things by setting the override to unreasonable
+  // values via about:config
+  if (!EncodingUtils::FindEncodingForLabel(override, mFallback) ||
+      !EncodingUtils::IsAsciiCompatible(mFallback) ||
+      mFallback.EqualsLiteral("UTF-8")) {
+    mFallback.Truncate();
+  }
+
+  if (!mFallback.IsEmpty()) {
+    aFallback = mFallback;
+    return;
+  }
+
+  nsAutoCString locale;
+  nsCOMPtr<nsIXULChromeRegistry> registry =
+    mozilla::services::GetXULChromeRegistryService();
+  if (registry) {
+    registry->GetSelectedLocale(NS_LITERAL_CSTRING("global"), locale);
+  }
+
+  // Let's lower case the string just in case unofficial language packs
+  // don't stick to conventions.
+  ToLowerCase(locale); // ASCII lowercasing with CString input!
+
+  // Special case Traditional Chinese before throwing away stuff after the
+  // language itself. Today we only ship zh-TW, but be defensive about
+  // possible future values.
+  if (locale.EqualsLiteral("zh-tw") ||
+      locale.EqualsLiteral("zh-hk") ||
+      locale.EqualsLiteral("zh-mo") ||
+      locale.EqualsLiteral("zh-hant")) {
+    mFallback.AssignLiteral("Big5");
+    aFallback = mFallback;
+    return;
+  }
+
+  // Throw away regions and other variants to accommodate weird stuff seen
+  // in telemetry--apparently unofficial language packs.
+  int32_t index = locale.FindChar('-');
+  if (index >= 0) {
+    locale.Truncate(index);
+  }
+
+  if (NS_FAILED(nsUConvPropertySearch::SearchPropertyValue(
+      localesFallbacks, ArrayLength(localesFallbacks), locale, mFallback))) {
+    mFallback.AssignLiteral("windows-1252");
+  }
+
+  aFallback = mFallback;
+}
+
+void
+FallbackEncoding::FromLocale(nsACString& aFallback)
+{
+  MOZ_ASSERT(FallbackEncoding::sInstance,
+             "Using uninitialized fallback cache.");
+  FallbackEncoding::sInstance->Get(aFallback);
+}
+
+// PrefChangedFunc
+void
+FallbackEncoding::PrefChanged(const char*, void*)
+{
+  MOZ_ASSERT(FallbackEncoding::sInstance,
+             "Pref callback called with null fallback cache.");
+  FallbackEncoding::sInstance->Invalidate();
+}
+
+void
+FallbackEncoding::Initialize()
+{
+  MOZ_ASSERT(!FallbackEncoding::sInstance,
+             "Initializing pre-existing fallback cache.");
+  FallbackEncoding::sInstance = new FallbackEncoding;
+  Preferences::RegisterCallback(FallbackEncoding::PrefChanged,
+                                "intl.charset.fallback.override",
+                                nullptr);
+  Preferences::RegisterCallback(FallbackEncoding::PrefChanged,
+                                "general.useragent.locale",
+                                nullptr);
+  Preferences::AddBoolVarCache(&sGuessFallbackFromTopLevelDomain,
+                               "intl.charset.fallback.tld");
+}
+
+void
+FallbackEncoding::Shutdown()
+{
+  MOZ_ASSERT(FallbackEncoding::sInstance,
+             "Releasing non-existent fallback cache.");
+  delete FallbackEncoding::sInstance;
+  FallbackEncoding::sInstance = nullptr;
+}
+
+bool
+FallbackEncoding::IsParticipatingTopLevelDomain(const nsACString& aTLD)
+{
+  nsAutoCString dummy;
+  return NS_FAILED(nsUConvPropertySearch::SearchPropertyValue(
+      nonParticipatingDomains,
+      ArrayLength(nonParticipatingDomains),
+      aTLD,
+      dummy));
+}
+
+void
+FallbackEncoding::FromTopLevelDomain(const nsACString& aTLD,
+                                     nsACString& aFallback)
+{
+  if (NS_FAILED(nsUConvPropertySearch::SearchPropertyValue(
+      domainsFallbacks, ArrayLength(domainsFallbacks), aTLD, aFallback))) {
+    aFallback.AssignLiteral("windows-1252");
+  }
+}
+
+} // namespace dom
+} // namespace mozilla