This CL adds a tool that can compare the class hierarchies of two dill files.
Currently it only checks for public classes and their public supertypes.
We could extend the tool later if needed.
Currently it gives this for flutter:
```
$ out/ReleaseX64/dart pkg/kernel/bin/compare_hierarchies.dart /path/to/flutter/bin/cache/flutter_web_sdk/kernel/flutter_ddc_sdk_sound.dill /path/to/flutter/bin/cache/artifacts/engine/common/flutter_patched_sdk/platform_strong.dill "dart:nativewrappers#NativeFieldWrapperClass1"
(1): /path/to/flutter/bin/cache/flutter_web_sdk/kernel/flutter_ddc_sdk_sound.dill
(2): /path/to/flutter/bin/cache/artifacts/engine/common/flutter_patched_sdk/platform_strong.dill
Missing classes in lib dart:_internal
In (2) but not in (1): [VMLibraryHooks, Lists, VMInternalsForTesting, ClassID]
Missing classes in lib dart:ui
In (1) but not in (2): [PlatformViewRegistry]
Class(ColorFilter) in dart.ui from (2) has these extra supertypes: [ImageFilter (dart:ui)]
```
where the last line is https://github.com/dart-lang/sdk/issues/48245
It gives this for the dart sdk:
```
$ out/ReleaseX64/dart pkg/kernel/bin/compare_hierarchies.dart out/ReleaseX64/vm_platform_strong.dill out/ReleaseX64/ddc_platform_sound.dill "dart:nativewrappers#NativeFieldWrapperClass1"
(1): out/ReleaseX64/vm_platform_strong.dill
(2): out/ReleaseX64/ddc_platform_sound.dill
Missing classes in lib dart:_internal
In (1) but not in (2): [VMLibraryHooks, Lists, VMInternalsForTesting, ClassID]
```
which seems fine (dart:_internal after all)
Change-Id: I03c0dbcc3e5058a0c7d6a996b511cf6d449dd4f3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/231100
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>
Jens Johansen
0794821969