Swap setTraversalBefore to setTraversalAfter, since setTraversalBefore is broken. (flutter/engine#4656)

It seems that setTraversalBefore doesn't work as well as setTraversalAfter for some reason, although I'm using them the same way. Some apps would lock up TalkBack when traversing if setTraversalBefore was set, but not with the equivalent setTraversalAfter.

It's not entirely clear why this is, but I'm going with this to at least get it fixed for apps we know about.

Addresses flutter/flutter#14600

See also flutter/flutter#14607

engine/src/flutter/lib/ui/semantics.dart

@@ -399,7 +399,7 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
     String increasedValue,
     String decreasedValue,
     TextDirection textDirection,
-    int nextNodeId,
+    int previousNodeId,
     Float64List transform,
     Int32List children,
   }) {
@@ -423,7 +423,7 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
                 increasedValue,
                 decreasedValue,
                 textDirection != null ? textDirection.index + 1 : 0,
-                nextNodeId ?? -1,
+                previousNodeId ?? -1,
                 transform,
                 children,);
   }
@@ -446,7 +446,7 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
     String increasedValue,
     String decreasedValue,
     int textDirection,
-    int nextNodeId,
+    int previousNodeId,
     Float64List transform,
     Int32List children,
   ) native 'SemanticsUpdateBuilder_updateNode';

engine/src/flutter/lib/ui/semantics/semantics_node.h

@@ -76,7 +76,7 @@ struct SemanticsNode {
   std::string increasedValue;
   std::string decreasedValue;
   int32_t textDirection = 0;  // 0=unknown, 1=rtl, 2=ltr
-  int32_t nextNodeId = -1;
+  int32_t previousNodeId = -1;
 
   SkRect rect = SkRect::MakeEmpty();
   SkMatrix44 transform = SkMatrix44(SkMatrix44::kIdentity_Constructor);

engine/src/flutter/lib/ui/semantics/semantics_update_builder.cc

@@ -52,7 +52,7 @@ void SemanticsUpdateBuilder::updateNode(int id,
                                         std::string increasedValue,
                                         std::string decreasedValue,
                                         int textDirection,
-                                        int nextNodeId,
+                                        int previousNodeId,
                                         const tonic::Float64List& transform,
                                         const tonic::Int32List& children) {
   SemanticsNode node;
@@ -71,7 +71,7 @@ void SemanticsUpdateBuilder::updateNode(int id,
   node.increasedValue = increasedValue;
   node.decreasedValue = decreasedValue;
   node.textDirection = textDirection;
-  node.nextNodeId = nextNodeId;
+  node.previousNodeId = previousNodeId;
   node.transform.setColMajord(transform.data());
   node.children = std::vector<int32_t>(
       children.data(), children.data() + children.num_elements());

engine/src/flutter/lib/ui/semantics/semantics_update_builder.h

@@ -43,7 +43,7 @@ class SemanticsUpdateBuilder
                   std::string increasedValue,
                   std::string decreasedValue,
                   int textDirection,
-                  int nextNodeId,
+                  int previousNodeId,
                   const tonic::Float64List& transform,
                   const tonic::Int32List& children);
 

engine/src/flutter/shell/platform/android/io/flutter/view/AccessibilityBridge.java

@@ -241,8 +241,8 @@ class AccessibilityBridge extends AccessibilityNodeProvider implements BasicMess
 
         result.setSelected(object.hasFlag(Flag.IS_SELECTED));
         result.setText(object.getValueLabelHint());
-        result.setTraversalBefore(mOwner,
-            object.nextNodeId == -1 ? View.NO_ID : object.nextNodeId);
+        result.setTraversalAfter(mOwner,
+            object.previousNodeId == -1 ? View.NO_ID : object.previousNodeId);
 
         // Accessibility Focus
         if (mA11yFocusedObject != null && mA11yFocusedObject.id == virtualViewId) {
@@ -693,7 +693,7 @@ class AccessibilityBridge extends AccessibilityNodeProvider implements BasicMess
         String decreasedValue;
         String hint;
         TextDirection textDirection;
-        int nextNodeId;
+        int previousNodeId;
 
         boolean hadPreviousConfig = false;
         int previousFlags;
@@ -746,7 +746,7 @@ class AccessibilityBridge extends AccessibilityNodeProvider implements BasicMess
         void log(String indent, boolean recursive) {
           Log.i(TAG, indent + "SemanticsObject id=" + id + " label=" + label + " actions=" +  actions + " flags=" + flags + "\n" +
                      indent + "  +-- textDirection=" + textDirection  + "\n"+
-                     indent + "  +-- nextNodeId=" + nextNodeId  + "\n"+
+                     indent + "  +-- previousNodeId=" + previousNodeId  + "\n"+
                      indent + "  +-- rect.ltrb=(" + left + ", " + top + ", " + right + ", " + bottom + ")\n" +
                      indent + "  +-- transform=" + Arrays.toString(transform) + "\n");
           if (children != null && recursive) {
@@ -793,7 +793,7 @@ class AccessibilityBridge extends AccessibilityNodeProvider implements BasicMess
 
             textDirection = TextDirection.fromInt(buffer.getInt());
 
-            nextNodeId = buffer.getInt();
+            previousNodeId = buffer.getInt();
 
             left = buffer.getFloat();
             top = buffer.getFloat();

engine/src/flutter/shell/platform/android/platform_view_android.cc

@@ -526,7 +526,7 @@ void PlatformViewAndroid::UpdateSemantics(
         strings.push_back(node.hint);
       }
       buffer_int32[position++] = node.textDirection;
-      buffer_int32[position++] = node.nextNodeId;
+      buffer_int32[position++] = node.previousNodeId;
       buffer_float32[position++] = node.rect.left();
       buffer_float32[position++] = node.rect.top();
       buffer_float32[position++] = node.rect.right();