Fix the snapshotter to generate valid precompilation snapshots

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 d783c8572dc7ea8fdd5fdd79e3100334a8f9ac32..af2bdb70bfb3c062a8c4e07c9c6a80752e633448 100644
--- a/runtime/bin/gen_snapshot.cc
+++ b/runtime/bin/gen_snapshot.cc
@@ -435,7 +435,11 @@ static Dart_Handle LoadSnapshotCreationScript(const char* script_name) {
   if (Dart_IsError(source)) {
     return source;
   }
-  return Dart_LoadLibrary(resolved_script_uri, source, 0, 0);
+  if (IsSnapshottingForPrecompilation()) {
+    return Dart_LoadScript(resolved_script_uri, source, 0, 0);
+  } else {
+    return Dart_LoadLibrary(resolved_script_uri, source, 0, 0);
+  }
 }