Require that injected members are private.

pkg/compiler/lib/src/patch_parser.dart

Index: pkg/compiler/lib/src/patch_parser.dart
diff --git a/pkg/compiler/lib/src/patch_parser.dart b/pkg/compiler/lib/src/patch_parser.dart
index 51295cef1b1d56631543f8c5d75eb446586c828c..1dd514fe29f8a32535659c0781d7ceb600a91d11 100644
--- a/pkg/compiler/lib/src/patch_parser.dart
+++ b/pkg/compiler/lib/src/patch_parser.dart
@@ -251,6 +251,9 @@ class PatchMemberListener extends MemberListener {
         // Skip this element.
       }
     } else {
+      if (Name.isPublicName(patch.name)) {
+        reporter.reportErrorMessage(patch, MessageKind.INJECTED_PUBLIC_MEMBER);
+      }
       enclosingClass.addMember(patch, reporter);
     }
   }
@@ -295,6 +298,9 @@ class PatchElementListener extends ElementListener implements Listener {
         // Skip this element.
       }
     } else {
+      if (Name.isPublicName(patch.name)) {
+        reporter.reportErrorMessage(patch, MessageKind.INJECTED_PUBLIC_MEMBER);
+      }
       compilationUnitElement.addMember(patch, reporter);
     }
   }