Bug 1729329 - Mark txUnionNodeTest::addNodeTest as infallible. r=farre

Differential Revision: https://phabricator.services.mozilla.com/D124665

dom/xslt/xpath/txExpr.h

@@ -817,9 +817,8 @@ class txNamedAttributeStep : public Expr {
  */
 class txUnionNodeTest : public txNodeTest {
  public:
-  nsresult addNodeTest(txNodeTest* aNodeTest) {
+  void addNodeTest(txNodeTest* aNodeTest) {
     mNodeTests.AppendElement(aNodeTest);
-    return NS_OK;
   }
 
   TX_DECL_NODE_TEST

dom/xslt/xpath/txXPathOptimizer.cpp

@@ -191,7 +191,6 @@ nsresult txXPathOptimizer::optimizeUnion(Expr* aInExpr, Expr** aOutExpr) {
   // Check for expressions like "foo | bar" and
   // "descendant::foo | descendant::bar"
 
-  nsresult rv;
   uint32_t current;
   Expr* subExpr;
   for (current = 0; (subExpr = uni->getSubExprAt(current)); ++current) {
@@ -222,16 +221,14 @@ nsresult txXPathOptimizer::optimizeUnion(Expr* aInExpr, Expr** aOutExpr) {
       // Create a txUnionNodeTest if needed
       if (!unionTest) {
         UniquePtr<txNodeTest> owner(unionTest = new txUnionNodeTest);
-        rv = unionTest->addNodeTest(currentStep->getNodeTest());
-        NS_ENSURE_SUCCESS(rv, rv);
+        unionTest->addNodeTest(currentStep->getNodeTest());
 
         currentStep->setNodeTest(unionTest);
         Unused << owner.release();
       }
 
       // Merge the nodetest into the union
-      rv = unionTest->addNodeTest(step->getNodeTest());
-      NS_ENSURE_SUCCESS(rv, rv);
+      unionTest->addNodeTest(step->getNodeTest());
 
       step->setNodeTest(nullptr);