Fix gen snapshot code to use Dart_LoadLibrary instead of Dart_LoadScript so that the root library v…

runtime/bin/gen_snapshot.cc

Index: runtime/bin/gen_snapshot.cc
diff --git a/runtime/bin/gen_snapshot.cc b/runtime/bin/gen_snapshot.cc
index 0e12574316a7e52d0471b8b1a5f70bb2b14ef963..e15e49c6662b76612b51ee10c78a89cd0d94afec 100644
--- a/runtime/bin/gen_snapshot.cc
+++ b/runtime/bin/gen_snapshot.cc
@@ -449,7 +449,7 @@ static Dart_Handle LoadSnapshotCreationScript(const char* script_name) {
   if (Dart_IsError(source)) {
     return source;
   }
-  return Dart_LoadScript(resolved_script_uri, source, 0, 0);
+  return Dart_LoadLibrary(resolved_script_uri, source, 0, 0);
 }