Auto merge of #19450 - asajeffrey:buildbot-perf-upload-to-s3, r=jdm

Upload buildbot perf data to S3.

<!-- Please describe your changes on the following line: -->

Upload performance data to S3.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because this is test infrastructure

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etc/ci/buildbot_steps.yml

@@ -113,7 +113,9 @@ linux-nightly:
   - env CC=gcc-5 CXX=g++-5 ./mach build --release
   - ./mach package --release
   - ./mach upload-nightly linux
-  - ./mach test-perf --submit
+  - ./mach test-perf
+  - python ./etc/ci/performance/download_buildbot_timings.py --verbose
+  - aws s3 sync --size-only --acl public-read ./etc/ci/performance/output s3://servo-perf
 
 android:
   - ./mach clean-nightlies --keep 3 --force

etc/ci/performance/download_buildbot_timings.py

@@ -12,8 +12,13 @@
 from math import floor
 import os
 
+SCRIPT_PATH = os.path.split(__file__)[0]
+
 
 def main():
+    default_output_dir = os.path.join(SCRIPT_PATH, 'output')
+    default_cache_dir = os.path.join(SCRIPT_PATH, '.cache')
+
     parser = argparse.ArgumentParser(
         description="Download buildbot metadata"
     )
@@ -29,19 +34,17 @@ def main():
                         "Default: http://build.servo.org/json/builders/{}/builds/{}")
     parser.add_argument("--cache-dir",
                         type=str,
-                        default='.cache',
-                        help="the directory to cache JSON files in. "
-                        "Default: .cache")
+                        default=default_cache_dir,
+                        help="the directory to cache JSON files in. Default: " + default_cache_dir)
     parser.add_argument("--cache-name",
                         type=str,
                         default='build-{}-{}.json',
                         help="the filename to cache JSON data in. "
                         "Default: build-{}-{}.json")
     parser.add_argument("--output-dir",
                         type=str,
-                        default='output',
-                        help="the directory to save the CSV data to. "
-                        "Default: output")
+                        default=default_output_dir,
+                        help="the directory to save the CSV data to. Default: " + default_output_dir)
     parser.add_argument("--output-name",
                         type=str,
                         default='builds-{}-{}.csv',