All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=633181

Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?keys=agxzfmNocm9tZXBlcmZyFAsSB0Fub21hbHkYgICgxtvitgoM,agxzfmNocm9tZXBlcmZyFAsSB0Fub21hbHkYgICghvu8uQoM,agxzfmNocm9tZXBlcmZyFAsSB0Fub21hbHkYgICgxqGxtQoM,agxzfmNocm9tZXBlcmZyFAsSB0Fub21hbHkYgICgxtu2rwoM


Bot(s) for this bug's original alert(s):

chromium-rel-mac-retina

Started bisect job https://chromeperf.appspot.com/buildbucket_job_status/9005529746159754736

Started bisect job https://chromeperf.appspot.com/buildbucket_job_status/9004248621139207024

===== BISECT JOB RESULTS =====
Status: completed


=== Bisection aborted ===
The bisect was aborted because The metric values for the initial "good" and "bad" revisions do not represent a clear regression.
Please contact the the team (see below) if you believe this is in error.

=== Warnings ===
The following warnings were raised by the bisect job:

 * Bisect failed to reproduce the regression with enough confidence.

===== TESTED REVISIONS =====
Revision         Mean    Std Dev  N   Good?
chromium@408380  676992  0.0      12  good
chromium@408405  676992  0.0      8   bad

Bisect job ran on: mac_retina_perf_bisect
Bug ID: 633181

Test Command: src/tools/perf/run_benchmark -v --browser=release --output-format=chartjson --upload-results --also-run-disabled-tests system_health.memory_desktop
Test Metric: browse_news-memory:chrome:all_processes:reported_by_chrome:sqlite:effective_size_avg/browse_news_reddit
Relative Change: 0.00%
Score: 0

Buildbot stdio: http://build.chromium.org/p/tryserver.chromium.perf/builders/mac_retina_perf_bisect/builds/1568
Job details: https://chromeperf.appspot.com/buildbucket_job_status/9004248621139207024


Not what you expected? We'll investigate and get back to you!
  https://chromeperf.appspot.com/bad_bisect?try_job_id=5311888611606528

| O O | Visit http://www.chromium.org/developers/speed-infra/perf-bug-faq
|  X  | for more information addressing perf regression bugs. For feedback,
| / \ | file a bug with component Tests>AutoBisect.  Thank you!

Started bisect job https://chromeperf.appspot.com/buildbucket_job_status/9003876354357740160

===== BISECT JOB RESULTS =====
Status: completed


=== Bisection aborted ===
The bisect was aborted because The metric values for the initial "good" and "bad" revisions do not represent a clear regression.
Please contact the the team (see below) if you believe this is in error.

=== Warnings ===
The following warnings were raised by the bisect job:

 * Bisect failed to reproduce the regression with enough confidence.

===== TESTED REVISIONS =====
Revision         Mean    Std Dev  N   Good?
chromium@408197  676992  0.0      12  good
chromium@408405  676992  0.0      8   bad

Bisect job ran on: mac_retina_perf_bisect
Bug ID: 633181

Test Command: src/tools/perf/run_benchmark -v --browser=release --output-format=chartjson --upload-results --also-run-disabled-tests system_health.memory_desktop
Test Metric: browse_news-memory:chrome:all_processes:reported_by_chrome:sqlite:effective_size_avg/browse_news_reddit
Relative Change: 0.00%
Score: 0

Buildbot stdio: http://build.chromium.org/p/tryserver.chromium.perf/builders/mac_retina_perf_bisect/builds/1593
Job details: https://chromeperf.appspot.com/buildbucket_job_status/9003876354357740160


Not what you expected? We'll investigate and get back to you!
  https://chromeperf.appspot.com/bad_bisect?try_job_id=5612953001263104

| O O | Visit http://www.chromium.org/developers/speed-infra/perf-bug-faq
|  X  | for more information addressing perf regression bugs. For feedback,
| / \ | file a bug with component Tests>AutoBisect.  Thank you!

This must have been due to some infrastructure change. It followed a symmetric improvement between r407984-r408043, so I'm going to mark this as WontFix.