fix noop toString() diagnostics

lib/web_ui/dev/create_simulator.dart

@@ -27,7 +27,7 @@ class CreateSimulatorCommand extends Command<bool> with ArgUtils<bool> {
         lock.minorVersion,
         lock.device,
       );
-      print('INFO: Simulator created ${simulator.toString()}');
+      print('INFO: Simulator created $simulator');
     } catch (e) {
       throw Exception('Error creating requested simulator. You can use Xcode '
           'to install more versions: XCode > Preferences > Components.'

lib/web_ui/dev/utils.dart

@@ -276,7 +276,7 @@ Future<void> runFlutter(
   if (exitCode != 0) {
     throw ToolExit(
       'ERROR: Failed to run $executable with '
-      'arguments ${arguments.toString()}. Exited with exit code $exitCode',
+      'arguments $arguments. Exited with exit code $exitCode',
       exitCode: exitCode,
     );
   }

lib/web_ui/test/text/line_breaker_test.dart

@@ -263,7 +263,7 @@ void testMain() {
               result.index,
               i,
               reason: 'Failed at test case number $t:\n'
-                  '${testCase.toString()}\n'
+                  '$testCase\n'
                   '"$text"\n'
                   '\nExpected line break at {$lastLineBreak - $i} but found line break at {$lastLineBreak - ${result.index}}.',
             );
@@ -283,7 +283,7 @@ void testMain() {
               result.index,
               greaterThan(i),
               reason: 'Failed at test case number $t:\n'
-                  '${testCase.toString()}\n'
+                  '$testCase\n'
                   '"$text"\n'
                   '\nUnexpected line break found at {$lastLineBreak - ${result.index}}.',
             );