Activate the service isolate for all precompiled tests.

runtime/bin/loader.h

Index: runtime/bin/loader.h
diff --git a/runtime/bin/loader.h b/runtime/bin/loader.h
index 16ced436de1e8a9f17431bd67b22ce45e7870a19..bab237bb01be9afccd6a4995755c4b5890354d72 100644
--- a/runtime/bin/loader.h
+++ b/runtime/bin/loader.h
@@ -20,6 +20,8 @@ class Loader {
   explicit Loader(IsolateData* isolate_data);
   ~Loader();
 
+  static void InitForSnapshot(const char* snapshot_uri);
+
   // A static tag handler that hides all usage of a loader for an isolate.
   static Dart_Handle LibraryTagHandler(Dart_LibraryTag tag,
                                        Dart_Handle library,