Add initial version of performance regression sheriffing documentation.

tools/perf/docs/perf_regression_sheriffing.md

+# Perf Regression Sheriffing
+
+The perf regression sheriff tracks performance regressions in Chrome's
+continuous integration tests. Note that a [new rotation](perf_bot_sheriffing.md)
+has been created to ensure the builds and tests stay green, so the perf
+regression sheriff role is now entirely focused on performance.
+
+## Key Responsibilities
+
+ * [Triage Regressions on the Perf Dashboard](#triage)
+ * [Follow up on Performance Regressions](#followup)
+ * [Give Feedback on our Infrastructure](#feedback)
+
+###<a name="triage"></a> Triage Regressions on the Perf Dashboard
+
+Open the perf dashboard [alerts page](https://chromeperf.appspot.com/alerts).
+
+In the upper right corner, **sign in with your Google account**. Signing in is
+important in order to be able to kick off bisect jobs, and see data from
+internal waterfalls.
+
+The page shows two lists; you are responsible for triaging
+**Performance Alerts**. The list can be sorted by clicking on the column header.
+When you click on the checkbox next to an alert, all the other alerts that
+occurred in the same revision range will be highlighted.
+
+Check the boxes next to the alerts you want to take a look at, and click the
+"Graph" button. You'll be taken to a page with a table at the top listing all
+the alerts that have an overlapping revision range with the one you chose, and
+below it the dashboard shows graphs of all the alerts checked in that table.
+
+1. **Look at the graph**.
+  * If the alert appears to be **within the noise**, click on the red
+    exclamation point icon for it in the graph and hit the "Invalid" button.
+  * If the alert is **if the alert is visibly to the left or the right of the
+    actual regression**, click on it and use the "nudge" menu to move it into
+    place.
+  * If there is a line labeled "ref" on the graph, that is the reference build.
+    It's an older version of Chrome, used to help us sort out whether a change
+    to the bot or test might have caused the graph to jump, rather than a real
+    performance regression. If **the ref build moved at the same time as the
+    alert**, click on the alert and hit the "Invalid" button.
+2. **Look at the other alerts** in the table to see if any should be grouped together.
+   Note that the bisect will automatically dupe bugs if it finds they have the
+   same culprit, so you don't need to be too aggressive about grouping alerts
+   that might not be related. Some signs alerts should be grouped together:
+  * If they're all in the same test suite
+  * If they all regressed the same metric (a lot of commonality in the Test
+    column)
+3. **Triage the group of alerts**. Check all the alerts you believe are related,
+  and press the triage button.
+    * If one of the alerts already has a bug id, click "existing bug" and use
+      that bug id.
+    * Otherwise click "new bug". Be sure to cc the
+      [test owner](http://go/perf-owners) on the bug.
+4. **Look at the revision range** for the regression. You can see it in the
+   tooltip on the graph. If you see any likely culprits, cc the authors on the
+   bug.
+5. **Optionally, kick off more bisects**. The perf dashboard will automatically
+   kick off a bisect for each bug you file. But if you think the regression is
+   much clearer on one platform, or a specific page of a page set, or you want
+   to see a broader revision range feel free to click on the alert on that graph
+   and kick off a bisect for it. There should be capacity to kick off as many
+   bisects as you feel are necessary to investigate; [give feedback](#feedback)
+   below if you feel that is not the case.
+
+###<a name="followup"></a> Follow up on Performance Regressions
+
+During your shift, you should try to follow up on each of the bugs you filed.
+Once you've triaged all the alerts, check to see if the bisects have come back,
+or if they failed. If the results came back, and a culprit was found, follow up
+with the CL author. If the bisects failed to update the bug with results, please
+file a bug on it (see [feedback](#feedback) links below).
+
+After your shift, please try to follow up on the bugs you filed weekly. Kick off
+new bisects if the previous ones failed, and if the bisect picks a likely
+culprit follow up to ensure the CL author addresses the problem. If you are
+certain that a specific CL caused a performance regression, and the author does
+not have an immediate plan to address the problem, please revert the CL.
+
+###<a name="feedback"></a> Give Feedback on our Infrastructure
+
+Perf regression sheriffs have their eyes on the perf dashboard and bisects
+more than anyone else, and their feedback is invaluable for making sure these
+tools are accurate and improving them. Please file bugs and feature requests
+as you see them:
+
+   * **Perf Dashboard**: Please use the red "Report Issue" link in the navbar.
+   * **Perf Bisect/Trybots**: If a bisect is identifying the wrong CL as culprit
+     or missing a clear culprit, or not reproducing what appears to be a clear
+     regression, please link the comment the bisect bot posted on the bug at
+     [go/bad-bisects](https://docs.google.com/spreadsheets/d/13PYIlRGE8eZzsrSocA3SR2LEHdzc8n9ORUoOE2vtO6I/edit#gid=0).
+     The team triages these regularly. If you spot a really clear bug (bisect
+     job red, bugs not being updated with bisect results) please file it in
+     crbug with label `Cr-Tests-AutoBisect`.
+   * **Noisy Tests**: Please file a bug in crbug with label `Cr-Tests-Telemetry`
+     and [cc the owner](http://go/perf-owners).