Identify text fields as such to a11y on Android (flutter#4299)

* Identify text fields as such to a11y on Android

* Add focus flag

lib/ui/semantics.dart

@@ -124,6 +124,8 @@ class SemanticsFlags {
   static const int _kIsCheckedIndex = 1 << 1;
   static const int _kIsSelectedIndex = 1 << 2;
   static const int _kIsButtonIndex = 1 << 3;
+  static const int _kIsTextFieldIndex = 1 << 4;
+  static const int _kIsFocusedIndex = 1 << 5;
 
   const SemanticsFlags._(this.index);
 
@@ -161,14 +163,27 @@ class SemanticsFlags {
   /// a button.
   static const SemanticsFlags isButton = const SemanticsFlags._(_kIsButtonIndex);
 
+  /// Whether the semantic node represents a text field.
+  ///
+  /// Text fields are announced as such and allow text input via accessibility
+  /// affordances.
+  static const SemanticsFlags isTextField = const SemanticsFlags._(_kIsTextFieldIndex);
+
+  /// Whether the semantic node currently holds the user's focus.
+  ///
+  /// The focused element is usually the current receiver of keyboard inputs.
+  static const SemanticsFlags isFocused = const SemanticsFlags._(_kIsFocusedIndex);
+
   /// The possible semantics flags.
   ///
   /// The map's key is the [index] of the flag and the value is the flag itself.
   static final Map<int, SemanticsFlags> values = const <int, SemanticsFlags>{
     _kHasCheckedStateIndex: hasCheckedState,
     _kIsCheckedIndex: isChecked,
     _kIsSelectedIndex: isSelected,
-    _kIsButtonIndex: isButton
+    _kIsButtonIndex: isButton,
+    _kIsTextFieldIndex: isTextField,
+    _kIsFocusedIndex: isFocused,
   };
 
   @override
@@ -182,6 +197,10 @@ class SemanticsFlags {
         return 'SemanticsFlags.isSelected';
       case _kIsButtonIndex:
         return 'SemanticsFlags.isButton';
+      case _kIsTextFieldIndex:
+        return 'SemanticsFlags.isTextField';
+      case _kIsFocusedIndex:
+        return 'SemanticsFlags.isFocused';
     }
     return null;
   }

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

@@ -57,6 +57,8 @@ class AccessibilityBridge extends AccessibilityNodeProvider implements BasicMess
     private static final int SEMANTICS_FLAG_IS_CHECKED = 1 << 1;
     private static final int SEMANTICS_FLAG_IS_SELECTED = 1 << 2;
     private static final int SEMANTICS_FLAG_IS_BUTTON = 1 << 3;
+    private static final int SEMANTICS_FLAG_IS_TEXT_FIELD = 1 << 4;
+    private static final int SEMANTICS_FLAG_IS_FOCUSED = 1 << 5;
 
     AccessibilityBridge(FlutterView owner) {
         assert owner != null;
@@ -95,9 +97,14 @@ public AccessibilityNodeInfo createAccessibilityNodeInfo(int virtualViewId) {
         result.setClassName("Flutter"); // TODO(goderbauer): Set proper class names
         result.setSource(mOwner, virtualViewId);
         result.setFocusable(object.isFocusable());
+        result.setFocused((object.flags & SEMANTICS_FLAG_IS_FOCUSED) != 0);
+
         if (mFocusedObject != null)
             result.setAccessibilityFocused(mFocusedObject.id == virtualViewId);
 
+        if ((object.flags & SEMANTICS_FLAG_IS_TEXT_FIELD) != 0)
+            result.setClassName("android.widget.EditText");
+
         if (object.parent != null) {
             assert object.id > 0;
             result.setParent(mOwner, object.parent.id);