The CHROME_HEADLESS environment variable is set when building and running tests on bots.

The python function pylib.constants.CheckOutputDirectory() checks this variable when CHROMIUM_OUTPUT_DIR or BUILDTYPE are not defined, in order to auto-detect the current Chromium output directory.

The logic is essentially:

  - Glob all files that match $CHROME_SRC_DIR/out/*/build.ninja
  - If there is only one such file, the use its directory as the new
    value for CHROMIUM_OUTPUT_DIR, otherwise, print an error.
 
According to jbudorick@, we should get rid of this magic, and ensure the bots always set CHROMIUM_OUTPUT_DIR properly before invoking the Python scripts used during the Android build instead.

This entry is to track the issue.