Fix gen_snapshot product mode build

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
diff --git a/runtime/include/dart_api.h b/runtime/include/dart_api.h
index 84b3afadf913e7a2b40e490b11ebb6da22115f88..ed19c9e2d4e41d6ea1c4d9f6f039319e329d24f2 100644
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -2931,6 +2931,13 @@ DART_EXPORT Dart_Handle Dart_GetClass(Dart_Handle library,
  */
 DART_EXPORT Dart_Handle Dart_LibraryUrl(Dart_Handle library);
 
+
+/**
+ * \return An array of libraries.
+ */
+DART_EXPORT Dart_Handle Dart_GetLoadedLibraries();
+
+
 DART_EXPORT Dart_Handle Dart_LookupLibrary(Dart_Handle url);
 /* TODO(turnidge): Consider returning Dart_Null() when the library is
  * not found to distinguish that from a true error case. */