[CFE] Incremental compiler + FFI crash reproduction

Run like
```
out/ReleaseX64/dart --enable-asserts pkg/front_end/test/incremental_suite.dart -DupdateExpectations=true -- incremental/crash_05
```

Crashes like this:
```
NoSuchMethodError: The getter 'iterator' was called on null.
Receiver: null
Tried calling: iterator
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
#1      computeStrongComponents.recursivelySearch (package:kernel/util/graph.dart:36:30)
#2      computeStrongComponents.recursivelySearch (package:kernel/util/graph.dart:41:26)
#3      computeStrongComponents (package:kernel/util/graph.dart:74:24)
#4      _FfiDefinitionTransformer.manualVisitInTopologicalOrder (package:vm/transformations/ffi_definitions.dart:131:33)
#5      transformLibraries (package:vm/transformations/ffi_definitions.dart:89:15)
#6      VmTarget.performModularTransformationsOnLibraries (package:vm/target/vm.dart:162:34)
#7      KernelTarget.runBuildTransformations (package:front_end/src/fasta/kernel/kernel_target.dart:1236:19)
#8      KernelTarget.buildComponent.<anonymous closure> (package:front_end/src/fasta/kernel/kernel_target.dart:372:7)
```

Run like
```
out/ReleaseX64/dart --enable-asserts pkg/front_end/test/incremental_suite.dart -DupdateExpectations=true -- incremental/crash_06
```

Crashes like this:
```
Class((whatnot)) not found in compoundCache
#0      new NativeTypeCfe (package:vm/transformations/ffi_definitions.dart:775:9)
#1      _FfiDefinitionTransformer._replaceFields (package:vm/transformations/ffi_definitions.dart:494:16)
#2      _FfiDefinitionTransformer.visitClassInTopologicalOrder (package:vm/transformations/ffi_definitions.dart:198:28)
#3      _FfiDefinitionTransformer.manualVisitInTopologicalOrder.<anonymous closure> (package:vm/transformations/ffi_definitions.dart:158:9)
#4      List.forEach (dart:core-patch/growable_array.dart:403:8)
#5      _FfiDefinitionTransformer.manualVisitInTopologicalOrder (package:vm/transformations/ffi_definitions.dart:134:25)
#6      transformLibraries (package:vm/transformations/ffi_definitions.dart:89:15)
#7      VmTarget.performModularTransformationsOnLibraries (package:vm/target/vm.dart:162:34)
```

Bug: #45899

Change-Id: I9d42ed16577a79c80f1c3bd77ee82a135d4e107c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/197740
Commit-Queue: Jens Johansen <jensj@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>

pkg/front_end/testcases/incremental.status

@@ -6,3 +6,7 @@
 
 # http://dartbug.com/41812#issuecomment-684825703
 strongmode_mixins_2: Crash
+
+# http://dartbug.com/45899
+crash_05: Crash
+crash_06: Crash

pkg/front_end/testcases/incremental/crash_05.yaml

@@ -0,0 +1,33 @@
+# Copyright (c) 2021, the Dart project authors. Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE.md file.
+
+# Reproduce a crash.
+
+type: newworld
+worlds:
+  - entry: main.dart
+    experiments: non-nullable
+    sources:
+      main.dart: |
+        import 'dart:ffi';
+        import 'lib.dart';
+        class X extends Struct {
+          external Y xx;
+        }
+      lib.dart: |
+        import 'dart:ffi';
+        class Y extends Struct {
+          @Uint32()
+          external int yy;
+        }
+    expectedLibraryCount: 2
+
+  - entry: main.dart
+    experiments: non-nullable
+    worldType: updated
+    expectInitializeFromDill: false
+    invalidate:
+      - main.dart
+    expectedLibraryCount: 2
+    expectsRebuildBodiesOnly: true

pkg/front_end/testcases/incremental/crash_05.yaml.world.1.expect

@@ -0,0 +1,62 @@
+main = <No Member>;
+library from "org-dartlang-test:///lib.dart" as lib {
+
+  import "dart:ffi";
+
+  @#C6
+  class Y extends dart.ffi::Struct {
+    static final field dart.core::int* #sizeOf = (#C8).{dart.core::List::[]}(dart.ffi::_abi())/*isLegacy*/;
+    synthetic constructor •() → lib::Y
+      : super dart.ffi::Struct::•()
+      ;
+    constructor #fromTypedDataBase(dart.core::Object #typedDataBase) → lib::Y
+      : super dart.ffi::Struct::_fromTypedDataBase(#typedDataBase)
+      ;
+    @#C9
+    get yy() → dart.core::int
+      return dart.ffi::_loadUint32(this.{dart.ffi::_Compound::_typedDataBase}, (#C11).{dart.core::List::[]}(dart.ffi::_abi()));
+    @#C9
+    set yy(dart.core::int #externalFieldValue) → void
+      return dart.ffi::_storeUint32(this.{dart.ffi::_Compound::_typedDataBase}, (#C11).{dart.core::List::[]}(dart.ffi::_abi()), #externalFieldValue);
+  }
+}
+library from "org-dartlang-test:///main.dart" as main {
+
+  import "dart:ffi";
+  import "org-dartlang-test:///lib.dart";
+
+  @#C15
+  class X extends dart.ffi::Struct {
+    static final field dart.core::int* #sizeOf = (#C8).{dart.core::List::[]}(dart.ffi::_abi())/*isLegacy*/;
+    synthetic constructor •() → main::X
+      : super dart.ffi::Struct::•()
+      ;
+    constructor #fromTypedDataBase(dart.core::Object #typedDataBase) → main::X
+      : super dart.ffi::Struct::_fromTypedDataBase(#typedDataBase)
+      ;
+    get xx() → lib::Y
+      return new lib::Y::#fromTypedDataBase( block {
+        dart.core::Object #typedDataBase = this.{dart.ffi::_Compound::_typedDataBase};
+        dart.core::int #offset = (#C11).{dart.core::List::[]}(dart.ffi::_abi());
+      } =>#typedDataBase is dart.ffi::Pointer<dynamic> ?{dart.core::Object} dart.ffi::_fromAddress<lib::Y>(#typedDataBase.{dart.ffi::Pointer::address}.{dart.core::num::+}(#offset)) : let dart.typed_data::TypedData #typedData = dart._internal::unsafeCast<dart.typed_data::TypedData>(#typedDataBase) in #typedData.{dart.typed_data::TypedData::buffer}.{dart.typed_data::ByteBuffer::asUint8List}(#typedData.{dart.typed_data::TypedData::offsetInBytes}.{dart.core::num::+}(#offset), (#C8).{dart.core::List::[]}(dart.ffi::_abi())));
+    set xx(lib::Y #externalFieldValue) → void
+      return dart.ffi::_memCopy(this.{dart.ffi::_Compound::_typedDataBase}, (#C11).{dart.core::List::[]}(dart.ffi::_abi()), #externalFieldValue.{dart.ffi::_Compound::_typedDataBase}, #C10, (#C8).{dart.core::List::[]}(dart.ffi::_abi()));
+  }
+}
+constants  {
+  #C1 = "vm:ffi:struct-fields"
+  #C2 = TypeLiteralConstant(dart.ffi::Uint32)
+  #C3 = <dart.core::Type>[#C2]
+  #C4 = null
+  #C5 = dart.ffi::_FfiStructLayout {fieldTypes:#C3, packing:#C4}
+  #C6 = dart.core::pragma {name:#C1, options:#C5}
+  #C7 = 4
+  #C8 = <dart.core::int*>[#C7, #C7, #C7]
+  #C9 = dart.ffi::Uint32 {}
+  #C10 = 0
+  #C11 = <dart.core::int*>[#C10, #C10, #C10]
+  #C12 = TypeLiteralConstant(lib::Y)
+  #C13 = <dart.core::Type>[#C12]
+  #C14 = dart.ffi::_FfiStructLayout {fieldTypes:#C13, packing:#C4}
+  #C15 = dart.core::pragma {name:#C1, options:#C14}
+}

pkg/front_end/testcases/incremental/crash_06.yaml

@@ -0,0 +1,30 @@
+# Copyright (c) 2021, the Dart project authors. Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE.md file.
+
+# Reproduce a crash.
+
+type: newworld
+worlds:
+  - entry: structs.dart
+    experiments: non-nullable
+    sources:
+      structs.dart: |
+        import 'dart:ffi';
+        class A extends Struct {
+          external Y yy;
+        }
+        class Y extends Struct {
+          external Z zz;
+        }
+    expectedLibraryCount: 1
+
+  - entry: structs.dart
+    experiments: non-nullable
+    worldType: updated
+    expectInitializeFromDill: false
+    invalidate:
+      - structs.dart
+    expectedLibraryCount: 1
+    expectsRebuildBodiesOnly: true
+