Enables (temporarily) adb trace for sharded perf tests.

build/android/bb_run_sharded_steps.py

Index: build/android/bb_run_sharded_steps.py
diff --git a/build/android/bb_run_sharded_steps.py b/build/android/bb_run_sharded_steps.py
index 9b768a9f7e6214934b46483b365583efadef4101..086a3a13e3154c9858ba6ff6178e72ffedf9f88d 100755
--- a/build/android/bb_run_sharded_steps.py
+++ b/build/android/bb_run_sharded_steps.py
@@ -54,6 +54,7 @@ import os
 import signal
 import shutil
 import sys
+import time
 
 from pylib import android_commands
 from pylib import cmd_helper
@@ -174,6 +175,18 @@ def _KillPendingServers():
           os.kill(int(pid), signal.SIGQUIT)
         except Exception as e:
           logging.warning('Failed killing %s %s %s', server, pid, e)
+  # Restart the adb server with full trace, and redirect stderr to stdout
+  # so the extra tracing won't confuse higher up layers.
+  os.environ['ADB_TRACE'] = 'all'
+  cmd_helper.RunCmd(['adb', 'kill-server'])
+  cmd_helper.RunCmd(['adb', 'start-server'])
+  cmd_helper.RunCmd(['adb', 'root'])
+  i = 1
+  while not android_commands.GetAttachedDevices():
+    time.sleep(i)
+    i *= 2
+    if i > 10:
+      break
 
 
 def main(argv):