Bug 1526542 - Improve the efficiency of CreatePermissionKey(); r=baku

There are two changes being made here:

  * In call sites where we know both origin arguments are equal,
    we will call a specialized version of the function which
    avoids the origin equality check.
  * We avoid calling into the generic printf structure and build
    the result string manually.

Differential Revision: https://phabricator.services.mozilla.com/D19245

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

toolkit/components/antitracking/AntiTrackingCommon.cpp

@@ -121,17 +121,36 @@ bool GetParentPrincipalAndTrackingOrigin(
   return true;
 };
 
+void CreatePermissionKey(const nsCString& aTrackingOrigin,
+                         nsACString& aPermissionKey) {
+  MOZ_ASSERT(aPermissionKey.IsEmpty());
+
+  static const nsLiteralCString prefix =
+      NS_LITERAL_CSTRING(ANTITRACKING_PERM_KEY "^");
+
+  aPermissionKey.SetCapacity(prefix.Length() + aTrackingOrigin.Length());
+  aPermissionKey.Append(prefix);
+  aPermissionKey.Append(aTrackingOrigin);
+}
+
 void CreatePermissionKey(const nsCString& aTrackingOrigin,
                          const nsCString& aGrantedOrigin,
                          nsACString& aPermissionKey) {
+  MOZ_ASSERT(aPermissionKey.IsEmpty());
+
   if (aTrackingOrigin == aGrantedOrigin) {
-    aPermissionKey =
-        nsPrintfCString(ANTITRACKING_PERM_KEY "^%s", aTrackingOrigin.get());
+    CreatePermissionKey(aTrackingOrigin, aPermissionKey);
     return;
   }
 
-  aPermissionKey = nsPrintfCString(ANTITRACKING_PERM_KEY "^%s^%s",
-                                   aTrackingOrigin.get(), aGrantedOrigin.get());
+  static const nsLiteralCString prefix =
+      NS_LITERAL_CSTRING(ANTITRACKING_PERM_KEY "^");
+
+  aPermissionKey.SetCapacity(prefix.Length() + 1 + aTrackingOrigin.Length());
+  aPermissionKey.Append(prefix);
+  aPermissionKey.Append(aTrackingOrigin);
+  aPermissionKey.AppendLiteral("^");
+  aPermissionKey.Append(aGrantedOrigin);
 }
 
 // This internal method returns ACCESS_DENY if the access is denied,
@@ -1021,7 +1040,7 @@ bool AntiTrackingCommon::IsStorageAccessPermission(nsIPermission* aPermission,
   // shorter permission key and will then do a prefix match on the type of the
   // input permission to see if it is a storage access permission or not.
   nsAutoCString permissionKey;
-  CreatePermissionKey(origin, origin, permissionKey);
+  CreatePermissionKey(origin, permissionKey);
 
   nsAutoCString type;
   rv = aPermission->GetType(type);
@@ -1545,7 +1564,7 @@ bool AntiTrackingCommon::IsFirstPartyStorageAccessGrantedFor(
   }
 
   nsAutoCString type;
-  CreatePermissionKey(origin, origin, type);
+  CreatePermissionKey(origin, type);
 
   nsPermissionManager* permManager = nsPermissionManager::GetInstance();
   if (NS_WARN_IF(!permManager)) {