telemetry: Fix killing the perf profiler

tools/telemetry/telemetry/internal/backends/chrome/android_browser_backend.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import logging
 import sys
 
 from telemetry.core import exceptions
 from telemetry.internal.platform import android_platform_backend as \
   android_platform_backend_module
@@ skipping 123 matching lines @@
     args.append('--enable-remote-debugging')
     args.append('--disable-fre')
     args.append('--disable-external-intent-requests')
     return args
 
   @property
   def pid(self):
     pids = self.device.GetPids(self._backend_settings.package)
     if not pids or self._backend_settings.package not in pids:
       raise exceptions.BrowserGoneException(self.browser)
-    return int(pids[self._backend_settings.package])
+    if len(pids[self._backend_settings.package]) > 1:
+      raise Exception(
+          'At most one instance of process %s expected but found pids: '
+          '%s' % (self._backend_settings.package, pids))
+    return int(pids[self._backend_settings.package][0])
 
   @property
   def browser_directory(self):
     return None
 
   @property
   def profile_directory(self):
     return self._backend_settings.profile_dir
 
   @property
@@ skipping 23 matching lines @@
 
   def GetStandardOutput(self):
     return self.platform_backend.GetStandardOutput()
 
   def GetStackTrace(self):
     return self.platform_backend.GetStackTrace(self._target_arch)
 
   @property
   def should_ignore_certificate_errors(self):
     return not self.platform_backend.is_test_ca_installed