Fix accessibilityRole prop parsing

Summary:
During the refactor in D36889794 (https://github.com/facebook/react-native/commit/782e004e4943194c40f2fb15527fe99a61f69b88) and later D37050215 (https://github.com/facebook/react-native/commit/47280de85e62f33f0b97bc1ed7c83bc6ca0dc7d4) this block of code was erroneously deleted; add it back, because if the props iterator setter is disabled, nothing sets this property anymore.

Changelog: [Internal]

Reviewed By: ryancat, nscoding

Differential Revision: D37539700

fbshipit-source-id: 0850180721e0549fed6089cb278402c56eb9d627

ReactCommon/react/renderer/components/view/AccessibilityProps.cpp

@@ -166,7 +166,30 @@ AccessibilityProps::AccessibilityProps(
                                          rawProps,
                                          "testID",
                                          sourceProps.testId,
-                                         "")) {}
+                                         "")) {
+  // It is a (severe!) perf deoptimization to request props out-of-order.
+  // Thus, since we need to request the same prop twice here
+  // (accessibilityRole) we "must" do them subsequently here to prevent
+  // a regression. It is reasonable to ask if the `at` function can be improved;
+  // it probably can, but this is a fairly rare edge-case that (1) is easy-ish
+  // to work around here, and (2) would require very careful work to address
+  // this case and not regress the more common cases.
+  if (!enablePropIteratorSetter) {
+    const auto *rawPropValue =
+        rawProps.at("accessibilityRole", nullptr, nullptr);
+    AccessibilityTraits traits;
+    std::string roleString;
+    if (rawPropValue == nullptr || !rawPropValue->hasValue()) {
+      traits = AccessibilityTraits::None;
+      roleString = "";
+    } else {
+      fromRawValue(context, *rawPropValue, traits);
+      fromRawValue(context, *rawPropValue, roleString);
+    }
+    accessibilityTraits = traits;
+    accessibilityRole = roleString;
+  }
+}
 
 void AccessibilityProps::setProp(
     const PropsParserContext &context,