[Telemetry] Update android perf bot docs to include test trace information.

tools/perf/docs/perf_bot_sheriffing.md

 # Perf Bot Sheriffing
 
 The perf bot sheriff is responsible for keeping the bots on the chromium.perf
 waterfall up and running, and triaging performance test failures and flakes.
 
 **[Rotation calendar](https://calendar.google.com/calendar/embed?src=google.com_2fpmo740pd1unrui9d7cgpbg2k%40group.calendar.google.com)**
 
 ## Key Responsibilities
 
 *   [Handle Device and Bot Failures](#Handle-Device-and-Bot-Failures)
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 *   **Infra** label is appropriate for bugs that are not high priority, but we
     need infra team's help to triage. For example, the buildbot status page UI
     is weird or we are getting some infra-related log spam. The infra team works
     to triage these bugs within 24 hours, so you should ping if you do not get a
     response.
 *   **Tests>Telemetry** for telemetry failures.
 *   **Tests>AutoBisect** for bisect and perf try job failures.
 
  If you still need help, ask the speed infra chat, or escalate to sullivan@.
 
+### Android Cross-Device Failures
+
+Sometimes when looking at failing android tests you will notice that there are
+tests on multiple devices failing. Sometimes (but not always) this means that
+there is a problem on the host machine. One way this problem can occur is if
+a test is using the wrong version of adb in one of its commands. This causes
+the adb server on the host to reset which can cause failures to anything
+trying to communicate with a device via adb during that time. A good tool
+for diagnosing this is the **Test Trace** step on the android runs. This is a
+trace of which tests are running. If you have all the tests across all the
+testing shards failing, it may be an issue on the host not with the tests.
+This will no longer be used when the android bots move to swarming, since
+each device will be sandboxed from the others and not run from a single
+point.
+
+
 ### Clobbering
 
 Sometimes when a compile step is failing, you may be asked to clobber
 [example](https://bugs.chromium.org/p/chromium/issues/detail?id=598955#c7).
 Steps to clobber:
 
 1.  Open the builder page through
     [uberchromegw](https://uberchromegw.corp.google.com/i/chromium.perf).
 2.  At the bottom, there is a form titled **"Force build"**.
 3.  Fill out the force build form, including your username, the reason for the
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 **[Pri-2 bugs](https://bugs.chromium.org/p/chromium/issues/list?can=2&q=label%3APerformance-Sheriff-BotHealth+label%3APri-2)**
 are for disabled tests. These should be pinged weekly, and work towards fixing
 should be ongoing when the sheriff is not working on a Pri-1 issue. Here is the
 [list of Pri-2 bugs that have not been pinged in a week](https://bugs.chromium.org/p/chromium/issues/list?can=2&q=label:Performance-Sheriff-BotHealth%20label:Pri-2%20modified-before:today-7&sort=modified).
 
 <!-- Unresolved issues:
 1. Do perf sheriffs watch the bisect waterfall?
 2. Do perf sheriffs watch the internal clank waterfall?
 -->