Update material banner maxScaleFactor to meet GAR requirement (#142015)

fixes: flutter/flutter#142012

Author: hannah-hyj

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

@@ -17,6 +17,7 @@ import 'theme.dart';
 
 const Duration _materialBannerTransitionDuration = Duration(milliseconds: 250);
 const Curve _materialBannerHeightCurve = Curves.fastOutSlowIn;
+const double _kMaxContentTextScaleFactor = 1.5;
 
 /// Specify how a [MaterialBanner] was closed.
 ///
@@ -365,21 +366,31 @@ class _MaterialBannerState extends State<MaterialBanner> {
                       padding: leadingPadding,
                       child: widget.leading,
                     ),
-                  Expanded(
-                    child: DefaultTextStyle(
-                      style: textStyle!,
-                      child: widget.content,
+                  MediaQuery.withClampedTextScaling(
+                    // Set maximum text scale factor to _kMaxContentTextScaleFactor for the
+                    // content to keep the visual hierarchy the same even with larger font
+                    // sizes.
+                    maxScaleFactor: _kMaxContentTextScaleFactor,
+                    child: Expanded(
+                      child: DefaultTextStyle(
+                        style: textStyle!,
+                        child: widget.content,
+                      ),
                     ),
                   ),
                   if (isSingleRow)
-                    actionsBar,
+                    MediaQuery.withClampedTextScaling(
+                      // Set maximum text scale factor to _kMaxContentTextScaleFactor for the
+                      // actionsBar to keep the visual hierarchy the same even with larger font
+                      // sizes.
+                      maxScaleFactor: _kMaxContentTextScaleFactor,
+                      child: actionsBar,
+                    ),
                 ],
               ),
             ),
-            if (!isSingleRow)
-              actionsBar,
-            if (elevation == 0)
-              Divider(height: 0, color: dividerColor),
+            if (!isSingleRow) actionsBar,
+            if (elevation == 0) Divider(height: 0, color: dividerColor),
           ],
         ),
       ),

packages/flutter/test/material/banner_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -236,6 +237,51 @@ void main() {
     expect(contentBottomLeft.dx, lessThan(actionsTopRight.dx));
   });
 
+    testWidgets('material banner content can scale and has maxScaleFactor', (WidgetTester tester) async {
+
+    const String label = 'A';
+    Widget buildApp({ required TextScaler textScaler }) {
+      return MaterialApp(
+        home: MediaQuery(
+          data: MediaQueryData(textScaler: textScaler),
+          child: MaterialBanner(
+            forceActionsBelow: true,
+            content: const SizedBox(child:Center(child:Text(label))),
+            actions: <Widget>[
+              TextButton(
+                child: const Text('B'),
+                onPressed: () { },
+              ),
+            ],
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildApp(textScaler: TextScaler.noScaling));
+    expect(find.text(label), findsOneWidget);
+
+    if (!kIsWeb || isCanvasKit) { // https://github.com/flutter/flutter/issues/99933
+      expect(tester.getSize(find.text(label)), const Size(14.25, 20.0));
+    }
+
+    await tester.pumpWidget(buildApp(textScaler: const TextScaler.linear(1.1)));
+    await tester.pumpAndSettle();
+    if (!kIsWeb || isCanvasKit) { // https://github.com/flutter/flutter/issues/99933
+      expect(_sizeAlmostEqual(tester.getSize(find.text(label)), const Size(15.65, 22.0)), true);
+    }
+
+    await tester.pumpWidget(buildApp(textScaler: const TextScaler.linear(1.5)));
+    if (!kIsWeb || isCanvasKit) { // https://github.com/flutter/flutter/issues/99933
+      expect(_sizeAlmostEqual(tester.getSize(find.text(label)), const Size(21.25, 30)), true);
+    }
+
+    await tester.pumpWidget(buildApp(textScaler: const TextScaler.linear(4)));
+    if (!kIsWeb || isCanvasKit) { // https://github.com/flutter/flutter/issues/99933
+      expect(_sizeAlmostEqual(tester.getSize(find.text(label)), const Size(21.25, 30)), true);
+    }
+  });
+
   group('MaterialBanner elevation', () {
     Widget buildBanner(Key tapTarget, {double? elevation, double? themeElevation}) {
       return MaterialApp(
@@ -1117,3 +1163,7 @@ Material _getMaterialFromText(WidgetTester tester, String text) {
 RenderParagraph _getTextRenderObjectFromDialog(WidgetTester tester, String text) {
   return tester.element<StatelessElement>(find.descendant(of: find.byType(MaterialBanner), matching: find.text(text))).renderObject! as RenderParagraph;
 }
+
+bool _sizeAlmostEqual(Size a, Size b, {double maxDiff=0.05}) {
+  return (a.width - b.width).abs() <= maxDiff && (a.height - b.height).abs() <= maxDiff;
+}