Update TextEditingValue.selection on selection change (#9284)

Fixes a bug where tapping in the text under edit moved the cursor but
did not push the updated selection to the engine.

Adds a test for caret position updates.

packages/flutter/lib/src/widgets/editable_text.dart

@@ -381,12 +381,13 @@ class EditableTextState extends State<EditableText> implements TextInputClient {
   }
 
   void _handleSelectionChanged(TextSelection selection, RenderEditable renderObject, bool longPress) {
+    config.controller.selection = selection;
+
     // Note that this will show the keyboard for all selection changes on the
     // EditableWidget, not just changes triggered by user gestures.
     requestKeyboard();
 
     _hideSelectionOverlayIfNeeded();
-    config.controller.selection = selection;
 
     if (config.selectionControls != null) {
       _selectionOverlay = new TextSelectionOverlay(

packages/flutter/test/material/text_field_test.dart

@@ -191,6 +191,39 @@ void main() {
     await tester.pump();
   });
 
+  testWidgets('Caret position is updated on tap', (WidgetTester tester) async {
+    final TextEditingController controller = new TextEditingController();
+
+    Widget builder() {
+      return overlay(new Center(
+        child: new Material(
+          child: new TextField(
+            controller: controller,
+          ),
+        ),
+      ));
+    }
+
+    await tester.pumpWidget(builder());
+    expect(controller.selection.baseOffset, -1);
+    expect(controller.selection.extentOffset, -1);
+
+    final String testValue = 'abc def ghi';
+    await tester.enterText(find.byType(EditableText), testValue);
+    await tester.idle();
+
+    await tester.pumpWidget(builder());
+
+    // Tap to reposition the caret.
+    final int tapIndex = testValue.indexOf('e');
+    final Point ePos = textOffsetToPosition(tester, tapIndex);
+    await tester.tapAt(ePos);
+    await tester.pump();
+
+    expect(controller.selection.baseOffset, tapIndex);
+    expect(controller.selection.extentOffset, tapIndex);
+  });
+
   testWidgets('Can long press to select', (WidgetTester tester) async {
     final TextEditingController controller = new TextEditingController();