[flutter_tools] do not crash if chrome preference save fails (#66705)

Crash reporting shows at least one occurrence of this due to a windows file lock. That could happen if there is another running chrome instance, or perhaps a virus scanner is running. Print out the error and do not crash.

packages/flutter_tools/lib/src/web/chrome.dart

@@ -106,13 +106,14 @@ class ChromiumLauncher {
     @required OperatingSystemUtils operatingSystemUtils,
     @required BrowserFinder browserFinder,
     @required Logger logger,
+    @visibleForTesting FileSystemUtils fileSystemUtils,
   }) : _fileSystem = fileSystem,
        _platform = platform,
        _processManager = processManager,
        _operatingSystemUtils = operatingSystemUtils,
        _browserFinder = browserFinder,
        _logger = logger,
-       _fileSystemUtils = FileSystemUtils(
+       _fileSystemUtils = fileSystemUtils ?? FileSystemUtils(
          fileSystem: fileSystem,
          platform: platform,
        );
@@ -268,7 +269,13 @@ class ChromiumLauncher {
 
     if (sourceLocalStorageDir.existsSync()) {
       targetLocalStorageDir.createSync(recursive: true);
+      try {
         _fileSystemUtils.copyDirectorySync(sourceLocalStorageDir, targetLocalStorageDir);
+      } on FileSystemException catch (err) {
+        // This is a best-effort update. Display the message in case the failure is relevant.
+        // one possible example is a file lock due to multiple running chrome instances.
+        _logger.printError('Failed to save Chrome preferences: $err');
+      }
     }
   }
 

packages/flutter_tools/test/general.shard/web/chrome_test.dart

@@ -103,6 +103,45 @@ void main() {
     );
   });
 
+  testWithoutContext('does not crash if saving profile information fails due to a file system exception.', () async {
+    final MockFileSystemUtils fileSystemUtils = MockFileSystemUtils();
+    final BufferLogger logger = BufferLogger.test();
+    chromeLauncher = ChromiumLauncher(
+      fileSystem: fileSystem,
+      platform: platform,
+      processManager: processManager,
+      operatingSystemUtils: operatingSystemUtils,
+      browserFinder: findChromeExecutable,
+      logger: logger,
+      fileSystemUtils: fileSystemUtils,
+    );
+    when(fileSystemUtils.copyDirectorySync(any, any))
+      .thenThrow(const FileSystemException());
+    processManager.addCommand(const FakeCommand(
+      command: <String>[
+        'example_chrome',
+        '--user-data-dir=/.tmp_rand0/flutter_tools_chrome_device.rand0',
+        '--remote-debugging-port=1234',
+        ...kChromeArgs,
+        'example_url',
+      ],
+      stderr: kDevtoolsStderr,
+    ));
+
+    final Chromium chrome = await chromeLauncher.launch(
+      'example_url',
+      skipCheck: true,
+      cacheDir: fileSystem.currentDirectory,
+    );
+
+    // Create cache dir that the Chrome launcher will atttempt to persist.
+    fileSystem.directory('/.tmp_rand0/flutter_tools_chrome_device.rand0/Default/Local Storage')
+      .createSync(recursive: true);
+
+    await chrome.close(); // does not exit with error.
+    expect(logger.errorText, contains('Failed to save Chrome preferences'));
+  });
+
   testWithoutContext('can launch chrome with a custom debug port', () async {
     processManager.addCommand(const FakeCommand(
       command: <String>[
@@ -207,6 +246,7 @@ void main() {
   });
 }
 
+class MockFileSystemUtils extends Mock implements FileSystemUtils {}
 class MockOperatingSystemUtils extends Mock implements OperatingSystemUtils {}
 
 Future<Chromium> _testLaunchChrome(String userDataDir, FakeProcessManager processManager, ChromiumLauncher chromeLauncher) {