Stop importing js_helper.dart explicitly in the core library.

lib/compiler/implementation/patch_parser.dart

Index: lib/compiler/implementation/patch_parser.dart
diff --git a/lib/compiler/implementation/patch_parser.dart b/lib/compiler/implementation/patch_parser.dart
index 8e31e05162d8998ff459dcd50aa456a7c10b3d3e..f400c869e6c92c2149f4a740317a885f1ed132a4 100644
--- a/lib/compiler/implementation/patch_parser.dart
+++ b/lib/compiler/implementation/patch_parser.dart
@@ -143,6 +143,7 @@ class PatchParserTask extends leg.CompilerTask {
     // After scanning declarations, we handle the import tags in the patch.
     // TODO(lrn): These imports end up in the original library and are in
     // scope for the original methods too. This should be fixed.
+    compiler.importHelperLibrary(originLibrary);
     for (tree.LibraryTag tag in imports.toLink()) {
       compiler.scanner.importLibraryFromTag(tag,
                                             patchLibrary.entryCompilationUnit);