Bug 1575335 - Avoid creating an extra copy of the file name URI when checking whether the currently running script is from a tracker; r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D42706

--HG--
extra : moz-landing-system : lando

dom/base/Document.cpp

@@ -3573,8 +3573,14 @@ void Document::NoteScriptTrackingStatus(const nsACString& aURL,
   }
 }
 
-bool Document::IsScriptTracking(const nsACString& aURL) const {
-  return mTrackingScripts.Contains(aURL);
+bool Document::IsScriptTracking(JSContext* aCx) const {
+  JS::AutoFilename filename;
+  uint32_t line = 0;
+  uint32_t column = 0;
+  if (!JS::DescribeScriptedCaller(aCx, &filename, &line, &column)) {
+    return false;
+  }
+  return mTrackingScripts.Contains(nsDependentCString(filename.get()));
 }
 
 NS_IMETHODIMP

dom/base/Document.h

@@ -3904,11 +3904,13 @@ class Document : public nsINode,
   virtual AbstractThread* AbstractMainThreadFor(
       TaskCategory aCategory) override;
 
-  // The URLs passed to these functions should match what
-  // JS::DescribeScriptedCaller() returns, since these APIs are used to
+  // The URLs passed to this function should match what
+  // JS::DescribeScriptedCaller() returns, since this API is used to
   // determine whether some code is being called from a tracking script.
   void NoteScriptTrackingStatus(const nsACString& aURL, bool isTracking);
-  bool IsScriptTracking(const nsACString& aURL) const;
+  // The JSContext passed to this method represents the context that we want to
+  // determine if it belongs to a tracker.
+  bool IsScriptTracking(JSContext* aCx) const;
 
   // For more information on Flash classification, see
   // toolkit/components/url-classifier/flash-block-lists.rst

dom/fetch/Fetch.cpp

@@ -479,10 +479,7 @@ already_AddRefed<Promise> FetchRequest(nsIGlobalObject* aGlobal,
       loadGroup = doc->GetDocumentLoadGroup();
       cookieSettings = doc->CookieSettings();
 
-      nsAutoCString fileNameString;
-      if (nsJSUtils::GetCallingLocation(cx, fileNameString)) {
-        isTrackingFetch = doc->IsScriptTracking(fileNameString);
-      }
+      isTrackingFetch = doc->IsScriptTracking(cx);
     } else {
       principal = aGlobal->PrincipalOrNull();
       if (NS_WARN_IF(!principal)) {

dom/xhr/XMLHttpRequestMainThread.cpp

@@ -2426,12 +2426,8 @@ void XMLHttpRequestMainThread::MaybeLowerChannelPriority() {
   }
 
   JSContext* cx = jsapi.cx();
-  nsAutoCString fileNameString;
-  if (!nsJSUtils::GetCallingLocation(cx, fileNameString)) {
-    return;
-  }
 
-  if (!doc->IsScriptTracking(fileNameString)) {
+  if (!doc->IsScriptTracking(cx)) {
     return;
   }