feat(tool): Respect user-data-dir flag from web-browser-flag (flutter#169445)

### Respect user-data-dir flag from web-browser-flag

Currently, it's already possible to pass `web-browser-flag` when
launching Chrome, but the `user-data-dir` flag doesn't work as expected,
and there are some reasons for that.

In the implementation made in [PR
flutter#104935](flutter#104935), the
`web-browser-flag` is appended at the end of the Chrome launch
arguments.

For most scenarios, this works fine, as demonstrated in the Chrome unit
test below:

https://source.chromium.org/chromium/chromium/src/+/main:base/command_line_unittest.cc

```
TEST(CommandLineTest, MultipleSameSwitch) {
  const CommandLine::CharType* argv[] = {
      FILE_PATH_LITERAL("program"),
      FILE_PATH_LITERAL("--foo=one"),  // --foo first time
      FILE_PATH_LITERAL("-baz"),
      FILE_PATH_LITERAL("--foo=two")   // --foo second time
  };
  CommandLine cl(std::size(argv), argv);

  EXPECT_TRUE(cl.HasSwitch("foo"));
  EXPECT_TRUE(cl.HasSwitch("baz"));

  EXPECT_EQ("two", cl.GetSwitchValueASCII("foo"));
}
```
In this scenario, the parser will consider the last occurrence of a
flag.

However, this behavior does not apply to certain flags, because Chrome
processes some of them based on the first occurrence, not the last. This
is the case for `--user-data-dir`, which is parsed very early during
Chrome startup.

The proposed code checks whether `--user-data-dir` was provided via
`web-browser-flag`, and if so, it uses that value instead of the default
`%temp%\flutter_tools_chrome_device.xpto` temporary directory.

This also resolve this comment:
flutter#104935 (comment)

Example: `launch.json`
```
{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "flutter",
      "request": "launch",
      "type": "dart"
    },
    {
      "name": "flutter (profile mode)",
      "request": "launch",
      "type": "dart",
      "flutterMode": "profile"
    },
    {
      "name": "flutter (release mode)",
      "request": "launch",
      "type": "dart",
      "flutterMode": "release"
    },
    {
      "name": "Flutter for web (hot reloadable)",
      "type": "dart",
      "request": "launch",
      "program": "lib/main.dart",
      "args": [
        "-d",
        "chrome",
        "--web-port=5000",
        "--web-experimental-hot-reload",
        "--web-browser-flag=--user-data-dir=D:\\_Desenv\\flutter_tests\\chrome_profile"
      ]
    }
  ]
}
```

`chrome://version`

| Before | After  |
|--------|--------|
|
![before](https://github.com/user-attachments/assets/b3f33419-fbf1-446e-a471-745df2e8c4f6)
|
![after](https://github.com/user-attachments/assets/ea74a203-c269-4ce1-8a9b-f97e9a4cdc78)
|

Folder
| Before | After  |
|--------|--------|
|
![before_files](https://github.com/user-attachments/assets/8522e60b-d0eb-4b66-a4b6-c2d6ed34c15b)
|
![after_files](https://github.com/user-attachments/assets/ff94b498-b319-474c-89e5-c55f6e1c4383)
|

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

<!-- Links -->
[Contributor Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview
[Tree Hygiene]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
[test-exempt]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md
[Features we expect every widget to implement]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes
[Discord]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md
[Data Driven Fixes]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md

Author: reynaldots

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

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:collection/collection.dart';
 import 'package:meta/meta.dart';
 import 'package:process/process.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart' hide StackTrace;
@@ -145,6 +146,31 @@ class ChromiumLauncher {
   /// The executable this launcher will use.
   String findExecutable() => _browserFinder(_platform, _fileSystem);
 
+  /// Creates a user data directory for Chrome based on provided flags or creates a temporary one.
+  ///
+  /// This method handles the creation of Chrome's user data directory in two ways:
+  /// 1. If webBrowserFlags contains a --user-data-dir flag, it uses that directory
+  /// 2. Otherwise, it creates a temporary directory in the system's temp location
+  ///
+  /// The user data directory is where Chrome stores user preferences, cookies,
+  /// and other session data. Using a temporary directory ensures a clean state
+  /// for each launch, while allowing custom directories through flags for
+  /// persistent configurations.
+  Directory _createUserDataDirectory(List<String> webBrowserFlags) {
+    if (webBrowserFlags.isNotEmpty) {
+      final String? userDataDirFlag = webBrowserFlags.firstWhereOrNull(
+        (String flag) => flag.startsWith('--user-data-dir='),
+      );
+
+      if (userDataDirFlag != null) {
+        final Directory userDataDir = _fileSystem.directory(userDataDirFlag.split('=')[1]);
+        webBrowserFlags.remove(userDataDirFlag);
+        return userDataDir;
+      }
+    }
+    return _fileSystem.systemTempDirectory.createTempSync('flutter_tools_chrome_device.');
+  }
+
   /// Launch a Chromium browser to a particular `host` page.
   ///
   /// [headless] defaults to false, and controls whether we open a headless or
@@ -189,9 +215,7 @@ class ChromiumLauncher {
       }
     }
 
-    final Directory userDataDir = _fileSystem.systemTempDirectory.createTempSync(
-      'flutter_tools_chrome_device.',
-    );
+    final Directory userDataDir = _createUserDataDirectory(webBrowserFlags);
 
     if (cacheDir != null) {
       // Seed data dir with previous state.

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

@@ -931,6 +931,30 @@ void main() {
       await chrome.close();
     },
   );
+
+  testWithoutContext('respects custom user data directory flag', () async {
+    const String customUserDataDir = '/custom/chrome/data/dir';
+    processManager.addCommand(
+      const FakeCommand(
+        command: <String>[
+          'example_chrome',
+          '--user-data-dir=$customUserDataDir',
+          '--remote-debugging-port=12345',
+          ...kChromeArgs,
+          'example_url',
+        ],
+        stderr: kDevtoolsStderr,
+      ),
+    );
+
+    await expectReturnsNormallyLater(
+      chromeLauncher.launch(
+        'example_url',
+        skipCheck: true,
+        webBrowserFlags: <String>['--user-data-dir=$customUserDataDir'],
+      ),
+    );
+  });
 }
 
 /// Fake chrome connection that fails to get tabs a few times.