WIP: Add custom platform library.

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 2557 matching lines @@
     "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"
+    "_internal": "_internal/js_runtime/lib/internal_patch.dart",
+    "custom": "_internal/js_runtime/lib/custom_patch.dart"

[Johnni Winther, 2016/06/23 12:45:15]

All these should be part of the .platform file.

   };
 
   @override
   Uri resolvePatchUri(String libraryName, Uri platformConfigUri) {
     String patchLocation = _patchLocations[libraryName];
     if (patchLocation == null) return null;
     return platformConfigUri.resolve(patchLocation);
   }
 
   @override
@@ skipping 538 matching lines @@
 
   @override
   void onImpactUsed(ImpactUseCase impactUse) {
     if (impactUse == DeferredLoadTask.IMPACT_USE && !supportSerialization) {
       // TODO(johnniwinther): Allow emptying when serialization has been
       // performed.
       resolution.emptyCache();
     }
   }
 }