Bug 1365478 - Use BoolVarCache to cache preferences in XMLHttpRequest, r=baku

dom/xhr/XMLHttpRequestMainThread.cpp

@@ -2948,7 +2948,7 @@ XMLHttpRequestMainThread::SendInternal(const BodyExtractorBase* aBody)
 
   mIsMappedArrayBuffer = false;
   if (mResponseType == XMLHttpRequestResponseType::Arraybuffer &&
-      Preferences::GetBool("dom.mapped_arraybuffer.enabled", true)) {
+      IsMappedArrayBufferEnabled()) {
     nsCOMPtr<nsIURI> uri;
     nsAutoCString scheme;
 
@@ -3049,6 +3049,40 @@ XMLHttpRequestMainThread::SendInternal(const BodyExtractorBase* aBody)
   return rv;
 }
 
+/* static */
+bool
+XMLHttpRequestMainThread::IsMappedArrayBufferEnabled()
+{
+  static bool sMappedArrayBufferAdded = false;
+  static bool sIsMappedArrayBufferEnabled;
+
+  if (!sMappedArrayBufferAdded) {
+    Preferences::AddBoolVarCache(&sIsMappedArrayBufferEnabled,
+                                 "dom.mapped_arraybuffer.enabled",
+                                 true);
+    sMappedArrayBufferAdded = true;
+  }
+
+  return sIsMappedArrayBufferEnabled;
+}
+
+/* static */
+bool
+XMLHttpRequestMainThread::IsLowercaseResponseHeader()
+{
+  static bool sLowercaseResponseHeaderAdded = false;
+  static bool sIsLowercaseResponseHeaderEnabled;
+
+  if (!sLowercaseResponseHeaderAdded) {
+    Preferences::AddBoolVarCache(&sIsLowercaseResponseHeaderEnabled,
+                                 "dom.xhr.lowercase_header.enabled",
+                                 false);
+    sLowercaseResponseHeaderAdded = true;
+  }
+
+  return sIsLowercaseResponseHeaderEnabled;
+}
+
 // http://dvcs.w3.org/hg/xhr/raw-file/tip/Overview.html#dom-xmlhttprequest-setrequestheader
 NS_IMETHODIMP
 XMLHttpRequestMainThread::SetRequestHeader(const nsACString& aName,
@@ -3767,7 +3801,7 @@ NS_IMETHODIMP XMLHttpRequestMainThread::
 nsHeaderVisitor::VisitHeader(const nsACString &header, const nsACString &value)
 {
   if (mXHR.IsSafeHeader(header, mHttpChannel)) {
-    if (!Preferences::GetBool("dom.xhr.lowercase_header.enabled", false)) {
+    if (!IsLowercaseResponseHeader()) {
       if(!mHeaderList.InsertElementSorted(HeaderEntry(header, value),
                                           fallible)) {
         return NS_ERROR_OUT_OF_MEMORY;

dom/xhr/XMLHttpRequestMainThread.h

@@ -306,6 +306,14 @@ private:
 
   void UnsuppressEventHandlingAndResume();
 
+  // Check pref "dom.mapped_arraybuffer.enabled" to make sure ArrayBuffer is
+  // supported.
+  static bool IsMappedArrayBufferEnabled();
+
+  // Check pref "dom.xhr.lowercase_header.enabled" to make sure lowercased
+  // response header is supported.
+  static bool IsLowercaseResponseHeader();
+
 public:
   virtual void
   Send(JSContext* /*aCx*/, ErrorResult& aRv) override