Load patches via callback.

sdk/lib/_internal/compiler/implementation/use_unused_api.dart

 // Copyright (c) 2012, 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 file.
 
 /// This file use methods that aren't used by dart2js.dart, but that we wish to
 /// keep anyway. This might be general API that isn't currently in use,
 /// debugging aids, or API only used for testing (see TODO below).
 
 library dart2js.use_unused_api;
 
@@ skipping 49 matching lines @@
   useJs(new js.Blob(null));
   useJs(new js.NamedFunction(null, null));
   useConcreteTypesInferrer(null);
   useColor();
   useFilenames();
   useSsa(null);
   useCodeBuffer(null);
   usedByTests();
   useElements(null, null);
   useIr(null, null);
+  useCompiler(null);
 }
 
 useApi() {
   api.ReadStringFromUri uri;
 }
 
 void useConstant(dart2jslib.Constant constant, dart2jslib.ConstantSystem cs) {
   constant.isObject;
   cs.isBool(constant);
 }
@@ skipping 144 matching lines @@
     ..visitExpression(null)
     ..visitFunctionDefinition(null)
     ..visitInvokeStatic(null)
     ..visitLetCont(null)
     ..visitNode(null)
     ..visitParameter(null);
   task
     ..hasIr(null)
     ..getIr(null);
 }
+
+useCompiler(dart2jslib.Compiler compiler) {
+  compiler.libraryLoader.reset();
+  compiler.libraryLoader.reuseLibrary(null);
+}