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pkg/compiler/lib/src/js_backend/backend.dart

Index: pkg/compiler/lib/src/js_backend/backend.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend.dart b/pkg/compiler/lib/src/js_backend/backend.dart
index c7b70d2dfcd83b6cf4436a9d0ddf7a5b17a98727..b637d3ea3bc9f1824f117a1e9dffcc6f316d7665 100644
--- a/pkg/compiler/lib/src/js_backend/backend.dart
+++ b/pkg/compiler/lib/src/js_backend/backend.dart
@@ -2077,7 +2077,10 @@ class JavaScriptBackend extends Backend {
 
   Future onLibraryScanned(LibraryElement library, LibraryLoader loader) {
     return super.onLibraryScanned(library, loader).then((_) {
-      if (library.isPlatformLibrary && !library.isPatched) {
+      if (library.isPlatformLibrary &&
+          // Don't patch library currently disallowed.
+          !library.isSynthesized &&
+          !library.isPatched) {
         // Apply patch, if any.
         Uri patchUri = compiler.resolvePatchUri(library.canonicalUri.path);
         if (patchUri != null) {