hzl@, can you take a look?

We're just now seeing multiple errors of a missing "bucket" param, and it looks like your recent change removed a default value, so maybe the scripts need to be updated too?

Builder link: https://uberchromegw.corp.google.com/i/chromium.android/builders/Android%20Cronet%20Marshmallow%2064bit%20Builder

Bot command:
python -u /b/build/slave/Android_Cronet_Marshmallow_64bit_Builder/build/src/build/android/pylib/results/presentation/test_results_presentation.py --json-file /tmp/tmpr_5oaD.json --test-name cronet_sample_test_apk --builder-name 'Android Cronet Marshmallow 64bit Builder' --build-number 8279

Error:
usage: test_results_presentation.py [-h] --json-file JSON_FILE
                                    [--cs-base-url CS_BASE_URL] --bucket
                                    BUCKET --builder-name BUILDER_NAME
                                    --build-number BUILD_NUMBER --test-name
                                    TEST_NAME [--server-url SERVER_URL]
                                    [--content-type {text/html,application/octet-stream}]
test_results_presentation.py: error: argument --bucket is required
step returned non-zero exit code: 2

Suspect CL: https://codereview.chromium.org/2799153008