Adds support for a new --web-header option to flutter run.
Creates a workaround for https://github.com/flutter/flutter/issues/127902
This PR allows adding additional headers for the flutter run web server. This is useful to add headers like Cross-Origin-Embedder-Policy and Cross-Origin-Opener-Policy without the use of a proxy server. These headers are required enable advanced web features. This approach provides flexibility to the developer to make use of the feature as they see fit and is backward-compatible. One tradeoff is that it increases the surface area to support for future changes to the flutter web server.
https://github.com/flutter/flutter/issues/127902 is not fully addressed by this change. The solution for that task will be more opinionated. This PR creates a general-purpose workaround for anyone who needs a solution sooner while the bigger solution is developed.
Support for FFI calls with `@Native external` functions through Native assets on MacOS and iOS. This enables bundling native code without any build-system boilerplate code.
For more info see:
* https://github.com/flutter/flutter/issues/129757
### Implementation details for MacOS and iOS.
Dylibs are bundled by (1) making them fat binaries if multiple architectures are targeted, (2) code signing these, and (3) copying them to the frameworks folder. These steps are done manual rather than via CocoaPods. CocoaPods would have done the same steps, but (a) needs the dylibs to be there before the `xcodebuild` invocation (we could trick it, by having a minimal dylib in the place and replace it during the build process, that works), and (b) can't deal with having no dylibs to be bundled (we'd have to bundle a dummy dylib or include some dummy C code in the build file).
The dylibs are build as a new target inside flutter assemble, as that is the moment we know what build-mode and architecture to target.
The mapping from asset id to dylib-path is passed in to every kernel compilation path. The interesting case is hot-restart where the initial kernel file is compiled by the "inner" flutter assemble, while after hot restart the "outer" flutter run compiled kernel file is pushed to the device. Both kernel files need to contain the mapping. The "inner" flutter assemble gets its mapping from the NativeAssets target which builds the native assets. The "outer" flutter run get its mapping from a dry-run invocation. Since this hot restart can be used for multiple target devices (`flutter run -d all`) it contains the mapping for all known targets.
### Example vs template
The PR includes a new template that uses the new native assets in a package and has an app importing that. Separate discussion in: https://github.com/flutter/flutter/issues/131209.
### Tests
This PR adds new tests to cover the various use cases.
* dev/devicelab/bin/tasks/native_assets_ios.dart
* Runs an example app with native assets in all build modes, doing hot reload and hot restart in debug mode.
* dev/devicelab/bin/tasks/native_assets_ios_simulator.dart
* Runs an example app with native assets, doing hot reload and hot restart.
* packages/flutter_tools/test/integration.shard/native_assets_test.dart
* Runs (incl hot reload/hot restart), builds, builds frameworks for iOS, MacOS and flutter-tester.
* packages/flutter_tools/test/general.shard/build_system/targets/native_assets_test.dart
* Unit tests the new Target in the backend.
* packages/flutter_tools/test/general.shard/ios/native_assets_test.dart
* packages/flutter_tools/test/general.shard/macos/native_assets_test.dart
* Unit tests the native assets being packaged on a iOS/MacOS build.
It also extends various existing tests:
* dev/devicelab/bin/tasks/module_test_ios.dart
* Exercises the add2app scenario.
* packages/flutter_tools/test/general.shard/features_test.dart
* Unit test the new feature flag.
Update test expectations from application/javascript -> text/javascript
`package:mime` now uses `text/javascript` and not `application/javascript`.
See https://github.com/dart-lang/mime/pull/76.
See https://datatracker.ietf.org/doc/html/rfc9239.
> This document defines equivalent processing requirements for the various script media types. The most widely supported media type in use is `text/javascript`; all others are considered historical and obsolete aliases of `text/javascript`.
* Provide flutter sdk kernel files to dwds launcher instead of dart ones
* Update log test to report all warnings
* Update licences for new files
* Addressed CR comments
* Addressed CR comments
Building an application for a desktop platform that transitively included any Dart-based plugins (such as path_provider) broke `flutter test`, because its compilation was overriding the provided main (in this case, the test main) with `generated_main.dart` if it was present. This PR:
- Changes the `flutter test` compilation path to update `generated_main.dart`, so that the tests will work, and will include any registered Dart plugins.
- Makes using `generated_main.dart` during recompile opt-in, to try to reduce the chance of a similar bug happening with other codepaths in the future.
Fixes https://github.com/flutter/flutter/issues/88794
