To sync the libyuv checkout to an upstream revision, do the following:

These commands are known to work from the external/libyuv directory of the
Android tree's checkout.

Step 1: Remove the files/ subdirectory.

$ rm -rf files

Step 2: Clone the libyuv repository from upstream.

$ git clone https://chromium.googlesource.com/libyuv/libyuv files

Step 3 (optional): Checkout a specific commit/tag.

$ cd files
$ git checkout <commit_or_tag>
$ cd ..

Step 4: Remove files that aren't necessary (Android.mk, .git and OWNERS).

$ rm files/Android.mk
$ rm -rf files/.git
$ find files/ -name "OWNERS" | xargs rm

Step 5: Update the version and last_upgrade_date fields in the METADATA file.

Step 6: Update README.version with the version (can be found in
        files/include/libyuv/version.h)

Step 7: If any local modifications are being done, update README.version and
        this file with updated instructions.

Step 8: Ensure that libyuv builds and camera and media related CTS tests are
        passing. If there are any linker errors about missing symbols, try
	updating frameworks/av/media/libstagefright/export.lds.