Bug 765168 - Remove the dependency of XHR::send on a cx parameter. r=smaug

Given the new bindings, I think this is dead code anyway modulo the pref.

content/base/public/nsContentUtils.h

@@ -1572,6 +1572,7 @@ public:
                                                       nsresult* aRv);
 
   static JSContext *GetCurrentJSContext();
+  static JSContext *GetSafeJSContext();
 
   /**
    * Case insensitive comparison between two strings. However it only ignores

content/base/src/nsContentUtils.cpp

@@ -5454,6 +5454,13 @@ nsContentUtils::GetCurrentJSContext()
   return cx;
 }
 
+/* static */
+JSContext *
+nsContentUtils::GetSafeJSContext()
+{
+  return sThreadJSContextStack->GetSafeJSContext();
+}
+
 /* static */
 nsresult
 nsContentUtils::ASCIIToLower(nsAString& aStr)

content/base/src/nsXMLHttpRequest.cpp

@@ -2680,12 +2680,27 @@ GetRequestBody(nsIVariant* aBody, JSContext *aCx, nsIInputStream** aResult,
 
     // ArrayBuffer?
     jsval realVal;
+    nsCxPusher pusher;
+    JSAutoEnterCompartment ac;
     JSObject* obj;
+
+    // If there's a context on the stack, we can just use it. Otherwise, we need
+    // to use the safe js context (and push it into the stack, so that it's
+    // visible to cx-less functions that we might call here).
+    JSContext* cx = nsContentUtils::GetCurrentJSContext();
+    if (!cx) {
+      cx = nsContentUtils::GetSafeJSContext();
+      if (!pusher.Push(cx)) {
+        return NS_ERROR_FAILURE;
+      }
+    }
+
     nsresult rv = aBody->GetAsJSVal(&realVal);
     if (NS_SUCCEEDED(rv) && !JSVAL_IS_PRIMITIVE(realVal) &&
         (obj = JSVAL_TO_OBJECT(realVal)) &&
-        (JS_IsArrayBufferObject(obj, aCx))) {
-      ArrayBuffer buf(aCx, obj);
+        ac.enter(cx, obj) &&
+        (JS_IsArrayBufferObject(obj, cx))) {
+      ArrayBuffer buf(cx, obj);
       return GetRequestBody(&buf, aResult, aContentType, aCharset);
     }
   }