Fix updating packages map on reload and add a regression test

runtime/bin/loader.cc

Index: runtime/bin/loader.cc
diff --git a/runtime/bin/loader.cc b/runtime/bin/loader.cc
index f35c7076e9491a66bb876e74c5432cba8fc98117..de82be482639d729dd82c52a08cf82a723711f37 100644
--- a/runtime/bin/loader.cc
+++ b/runtime/bin/loader.cc
@@ -652,7 +652,15 @@ Dart_Handle Loader::LibraryTagHandler(Dart_LibraryTag tag,
   IsolateData* isolate_data =
       reinterpret_cast<IsolateData*>(Dart_CurrentIsolateData());
   ASSERT(isolate_data != NULL);
-
+  if ((tag == Dart_kScriptTag) && Dart_IsString(library)) {
+    // Update packages file for isolate.
+    const char* packages_file = NULL;
+    Dart_Handle result = Dart_StringToCString(library, &packages_file);
+    if (Dart_IsError(result)) {
+      return result;
+    }
+    isolate_data->UpdatePackagesFile(packages_file);
+  }
   // Grab this isolate's loader.
   Loader* loader = NULL;