Always precheck that the PreparseData has data before serializing it.

Drive-by-fix:
- rename preparsed_scope_data_builder_ to preparse_data_builder_

Change-Id: I8e709af8f69db44e03caa9132f06a7b8c906bfdb
Reviewed-on: https://chromium-review.googlesource.com/c/1387305Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58635}