How to update lzma_sdk:

1. Pick the version number to which you wish to update; for example, the current
   release on https://github.com/ip7z/7zip/releases (which is
   https://github.com/ip7z/7zip/releases/latest).

2. Find the download link for the "7zNNNN-src.tar.xz" asset, where "NNNN" is the
   version number without a period (e.g., "7z2601-src.tar.xz" for version
   26.01).

3. Create a CL for the file 3pp/7z/3pp.pb that updates the "download_url" field
   to the link discovered above and the "version" to the version chosen above,
   send it for review, and submit it. See https://crrev.com/c/7807444 for an
   example.

4. After the 3pp system has generated new binaries from those sources, browse
   https://chrome-infra-packages.appspot.com/p/infra/3pp/tools/7z/windows-amd64
   to find the version tag for the new binaries; for example, "version:3@26.01".

5. Create a new git branch on which to work:
   git new-branch lzma

6. In //DEPS, change the "version" field to this new version for both the
   host_platform and win64 7z entries.

7. From the GitHub release chosen above, download the asset file matching the
   pattern "lzmaNNNN.7z" where "NNNN" is the version number without a period
   (e.g., "lzma2601.7z" for version 26.01).

8. Expand the archive into a subdirectory of third_party/lzma_sdk:
   ( mkdir third_party/lzma_sdk/lzma2601 && cd third_party/lzma_sdk/lzma2601 \
       && ../bin/host_platform/7za x ~/Downloads/lzma2601.7z )

9. Convert line endings of the extracted text files:
   find third_party/lzma_sdk/lzma2601 -name bin -prune -o -type f \
       ! -name \*.ico -print0 | xargs -0 dos2unix

10. Delete the src/ directory:
    rm -fr third_party/lzma_sdk/src

11. Create a new src/ directory:
    mkdir third_party/lzma_sdk/src

12. Copy Asm/, C/, and DOC/lzma-sdk.txt from the extracted archive into src/.
    For example:
    (cd third_party/lzma_sdk/lzma2601 && tar -cf - Asm DOC/lzma-sdk.txt C) | \
        (cd third_party/lzma_sdk/src && tar -xf -)

13. Delete the expanded archive.
    rm -fr third_party/lzma_sdk/lzma2601

14. Create a git commit for the upstream files:
    git add third_party/lzma_sdk/src && git ci -m "LZMA SDK 26.01"

15. Create a new branch for patch application:
    git co -b patch_chain

16. Apply the patches/*, fixing each in its own commit as necessary:
    git am third_party/lzma_sdk/patches/*

17. Build //chrome/test:unit_tests and run the 7zip reader tests:
    autoninja -C out/Default chrome/test:unit_tests && \
    out/Default/unit_tests --single-process-tests --gtest_filter=SevenZipReader\*

18. Regenerate the patch files:
    git format-patch lzma -o third_party/lzma_sdk/patches

19. Update the Version, Date, CPEPrefix, and version number and link in the
    description of third_party/lzma_sdk/README.chromium.

20. Commit:
    git add third_party/lzma_sdk && git ci -m patches

21. Move the main branch to the latest commit and delete the patch_chain branch:
    git co -B lzma && git br -d patch_chain

22. Squash everything to one commit:
    git squash-branch

23. Give the commit a proper description and upload for review:
    git ci --amend && git cl upload --commit-description=+ -d