VM: Fix snapshoting slow-down caused by 99c6a18a1bc2a4f13d8dd027a597fdca0f2d6e0c.

runtime/bin/vmservice/loader.dart

Index: runtime/bin/vmservice/loader.dart
diff --git a/runtime/bin/vmservice/loader.dart b/runtime/bin/vmservice/loader.dart
index 14b7a76eee7e5231cd58e711420705a283b5fdcf..b34e54c3309371b2e42b8bb6c93bc5fc526bb306 100644
--- a/runtime/bin/vmservice/loader.dart
+++ b/runtime/bin/vmservice/loader.dart
@@ -1035,12 +1035,13 @@ _processLoadRequest(request) {
         String packagesFile = request[5];
         String workingDirectory = request[6];
         String rootScript = request[7];
+        bool isReloading = request[8];
         if (loaderState == null) {
           loaderState = new IsolateLoaderState(isolateId);
           isolateEmbedderData[isolateId] = loaderState;
           loaderState.init(
               packageRoot, packagesFile, workingDirectory, rootScript);
-        } else {
+        } else if (isReloading) {
           loaderState.updatePackageMap(packagesFile);
         }
         loaderState.sp = sp;