Honor more of the Theme for CircleAvatar with backgroundColor (#12333)

packages/flutter/lib/src/material/circle_avatar.dart

@@ -5,9 +5,10 @@
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 
+import 'colors.dart';
 import 'constants.dart';
 import 'theme.dart';
-import 'typography.dart';
+import 'theme_data.dart';
 
 // Examples can assume:
 // String userAvatarUrl;
@@ -91,9 +92,19 @@ class CircleAvatar extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final ThemeData theme = Theme.of(context);
-    final TextStyle textStyle = backgroundColor != null ?
-        new Typography(platform: theme.platform).white.title :
-        theme.primaryTextTheme.title;
+    TextStyle textStyle = theme.primaryTextTheme.title;
+    if (foregroundColor != null) {
+      textStyle = textStyle.copyWith(color: foregroundColor);
+    } else if (backgroundColor != null) {
+      switch (ThemeData.estimateBrightnessForColor(backgroundColor)) {
+        case Brightness.dark:
+          textStyle = textStyle.copyWith(color: Colors.white);
+          break;
+        case Brightness.light:
+          textStyle = textStyle.copyWith(color: Colors.black);
+          break;
+      }
+    }
     return new AnimatedContainer(
       width: radius * 2.0,
       height: radius * 2.0,

packages/flutter/test/material/circle_avatar_test.dart

@@ -7,8 +7,8 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  testWidgets('CircleAvatar with background color', (WidgetTester tester) async {
-    final Color backgroundColor = Colors.blue.shade400;
+  testWidgets('CircleAvatar with dark background color', (WidgetTester tester) async {
+    final Color backgroundColor = Colors.blue.shade900;
     await tester.pumpWidget(
       wrap(
         child: new CircleAvatar(
@@ -30,6 +30,29 @@ void main() {
     expect(paragraph.text.style.color, equals(Colors.white));
   });
 
+  testWidgets('CircleAvatar with light background color', (WidgetTester tester) async {
+    final Color backgroundColor = Colors.blue.shade100;
+    await tester.pumpWidget(
+      wrap(
+        child: new CircleAvatar(
+          backgroundColor: backgroundColor,
+          radius: 50.0,
+          child: const Text('Z'),
+        ),
+      ),
+    );
+
+    final RenderConstrainedBox box = tester.renderObject(find.byType(CircleAvatar));
+    expect(box.size.width, equals(100.0));
+    expect(box.size.height, equals(100.0));
+    final RenderDecoratedBox child = box.child;
+    final BoxDecoration decoration = child.decoration;
+    expect(decoration.color, equals(backgroundColor));
+
+    final RenderParagraph paragraph = tester.renderObject(find.text('Z'));
+    expect(paragraph.text.style.color, equals(Colors.black));
+  });
+
   testWidgets('CircleAvatar with foreground color', (WidgetTester tester) async {
     final Color foregroundColor = Colors.red.shade100;
     await tester.pumpWidget(