Decouple WorkItem from Compiler

pkg/dart2js_incremental/lib/caching_compiler.dart

Index: pkg/dart2js_incremental/lib/caching_compiler.dart
diff --git a/pkg/dart2js_incremental/lib/caching_compiler.dart b/pkg/dart2js_incremental/lib/caching_compiler.dart
index 34f67c64fc824953f95fdd8b4850c04fe33d7fc9..8bf1c64127c6f97ce89ecba7785f6568d2b4797d 100644
--- a/pkg/dart2js_incremental/lib/caching_compiler.dart
+++ b/pkg/dart2js_incremental/lib/caching_compiler.dart
@@ -85,7 +85,7 @@ Future<CompilerImpl> reuseCompiler(
         // Likewise, always be prepared for runtimeType support.
         // TODO(johnniwinther): Add global switch to force RTI.
         compiler.resolverWorld.hasRuntimeTypeSupport = true;
-        backend.registerRuntimeType(compiler.enqueuer.resolution);
+        compiler.enqueuer.resolution.applyImpact(backend.registerRuntimeType());
         return compiler;
       });
     });