Download META/ab_partitions.txt from the target files zip.

[Databean]

The full target files zip file is not downloaded unless it is requested by other flags.

Bug: b/439877215

[cjreynol]

Rather than adding ReadableZip::Invalid to allow the target_files_zip to be the cross-condition variable, could we extract the ab_partitions.txt logic to be a helper we call in both blocks. Then we could have the resulting filepath be the shared variable. I think intentionally adding an invalid state is adding mental overhead to future updates, and in this case I think avoiding it does not make things worse.

Roughly thinking:

std::string ExtractAbPartitions(const std::string& target_directory, ReadableZip target_files) {
  //...
}

then the conditional becomes:

std::string ab_partitions_filepath;
if (...) {
  //...
  ReadableZip target_files = ...;
  ab_partitions_filepath = ExtractAbPartitions(target_directories.default_target_files, target_files);
} else {
  ReadableZip target_files = ...;
  ab_partitions_filepath = ExtractAbPartitions(...); 
}
CF_EXPECT(config.AddFilesToConfig(...));

[Databean]

Thanks for the call out.

I forgot that I had already made this PR earlier and rewrote this code in #1738 . It doesn't include ReadableZip::Invalid and instead uses a ? : operator to initialize the ReadableZip value.