Introduce "platform configurations" to replace categories and libraries.dart.

pkg/compiler/lib/src/js_backend/backend.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.
 
 part of js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 2559 matching lines @@
             yieldStarExpression: emitter.staticFunctionAccess(
                 helpers.yieldStar),
             bodyName: namer.deriveAsyncBodyName(name));
         break;
       default:
         assert(element.asyncMarker == AsyncMarker.SYNC);
         return code;
     }
     return rewriter.rewrite(code);
   }
+
+  /// The locations of js patch-files relative to the sdk-descriptors.
+  static const _patchLocations = const <String, String>{
+    "async": "_internal/js_runtime/lib/async_patch.dart",
+    "collection":  "_internal/js_runtime/lib/collection_patch.dart",
+    "convert": "_internal/js_runtime/lib/convert_patch.dart",
+    "core": "_internal/js_runtime/lib/core_patch.dart",
+    "developer": "_internal/js_runtime/lib/developer_patch.dart",
+    "io": "_internal/js_runtime/lib/io_patch.dart",
+    "isolate": "_internal/js_runtime/lib/isolate_patch.dart",
+    "math": "_internal/js_runtime/lib/math_patch.dart",
+    "mirrors": "_internal/js_runtime/lib/mirrors_patch.dart",
+    "typed_data": "_internal/js_runtime/lib/typed_data_patch.dart",
+    "_internal": "_internal/js_runtime/lib/internal_patch.dart"
+  };
+
+  @override
+  Uri resolvePatchUri(String libraryName, Uri platformConfigUri) {
+    String patchLocation = _patchLocations[libraryName];
+    if (patchLocation == null) return null;
+    return platformConfigUri.resolve(patchLocation);
+  }
 }
 
 /// Handling of special annotations for tests.
 class Annotations {
   static final Uri PACKAGE_EXPECT =
       new Uri(scheme: 'package', path: 'expect/expect.dart');
 
   final Compiler compiler;
 
   ClassElement expectNoInlineClass;
@@ skipping 411 matching lines @@
   }
 }
 
 /// Records that [constant] is used by the element behind [registry].
 class Dependency {
   final ConstantValue constant;
   final Element annotatedElement;
 
   const Dependency(this.constant, this.annotatedElement);
 }