change ThemeData.primaryColor to PrimarySwatch instead of PrimarySwatch[500] (#15265)

* change ThemeData.primaryColor to PrimarySwatch instead of PrimarySwatch[500]

* fix mismatched color in stock test case

examples/stocks/test/icon_color_test.dart

@@ -73,7 +73,7 @@ void main() {
     expect(find.text('Account Balance'), findsOneWidget);
 
     // check the colour of the icon - light mode
-    checkIconColor(tester, 'Stock List', Colors.purple.shade500); // theme primary color
+    checkIconColor(tester, 'Stock List', Colors.purple); // theme primary color
     checkIconColor(tester, 'Account Balance', Colors.black26); // disabled
     checkIconColor(tester, 'About', Colors.black45); // enabled
 

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

@@ -118,7 +118,7 @@ class ThemeData extends Diagnosticable {
     brightness ??= Brightness.light;
     final bool isDark = brightness == Brightness.dark;
     primarySwatch ??= Colors.blue;
-    primaryColor ??= isDark ? Colors.grey[900] : primarySwatch[500];
+    primaryColor ??= isDark ? Colors.grey[900] : primarySwatch;
     primaryColorBrightness ??= estimateBrightnessForColor(primaryColor);
     primaryColorLight ??= isDark ? Colors.grey[500] : primarySwatch[100];
     primaryColorDark ??= isDark ? Colors.black : primarySwatch[700];

packages/flutter/test/material/app_builder_test.dart

@@ -15,7 +15,7 @@ void main() {
       home: const Placeholder(),
       builder: (BuildContext context, Widget child) {
         log.add('build');
-        expect(Theme.of(context).primaryColor, Colors.green.shade500);
+        expect(Theme.of(context).primaryColor, Colors.green);
         expect(Directionality.of(context), TextDirection.ltr);
         expect(child, const isInstanceOf<Navigator>());
         return const Placeholder();
@@ -47,7 +47,7 @@ void main() {
         home: new Builder(
           builder: (BuildContext context) {
             log.add('build');
-            expect(Theme.of(context).primaryColor, Colors.yellow.shade500);
+            expect(Theme.of(context).primaryColor, Colors.yellow);
             expect(Directionality.of(context), TextDirection.rtl);
             return const Placeholder();
           },

packages/flutter/test/widgets/list_view_viewporting_test.dart

@@ -236,7 +236,7 @@ void main() {
 
     DecoratedBox widget = tester.firstWidget(find.byType(DecoratedBox));
     BoxDecoration decoration = widget.decoration;
-    expect(decoration.color, equals(Colors.blue[500]));
+    expect(decoration.color, equals(Colors.blue));
 
     setState(() {
       themeData = new ThemeData(primarySwatch: Colors.green);
@@ -246,7 +246,7 @@ void main() {
 
     widget = tester.firstWidget(find.byType(DecoratedBox));
     decoration = widget.decoration;
-    expect(decoration.color, equals(Colors.green[500]));
+    expect(decoration.color, equals(Colors.green));
   });
 
   testWidgets('ListView padding', (WidgetTester tester) async {