[Telemetry] Fix WPR files not being downloaded when required.

tools/telemetry/telemetry/unittest_util/system_stub.py

 # Copyright 2012 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.
 
 """Provides stubs for os, sys and subprocess for testing
 
 This test allows one to test code that itself uses os, sys, and subprocess.
 """
 
 import os
@@ skipping 164 matching lines @@
     pass
 
   def __init__(self):
     self.default_remote_paths = {CloudStorageModuleStub.INTERNAL_BUCKET:{},
                                  CloudStorageModuleStub.PARTNER_BUCKET:{},
                                  CloudStorageModuleStub.PUBLIC_BUCKET:{}}
     self.remote_paths = self.default_remote_paths
     self.local_file_hashes = {}
     self.local_hash_files = {}
     self.permission_level = CloudStorageModuleStub.INTERNAL_PERMISSION
+    self.downloaded_files = []
 
   def SetPermissionLevelForTesting(self, permission_level):
     self.permission_level = permission_level
 
   def CheckPermissionLevelForBucket(self, bucket):
     if bucket == CloudStorageModuleStub.PUBLIC_BUCKET:
       return
     elif (self.permission_level ==
           CloudStorageModuleStub.CREDENTIALS_ERROR_PERMISSION):
       raise CloudStorageModuleStub.CredentialsError()
@@ skipping 58 matching lines @@
   def GetHelper(self, bucket, remote_path, local_path, only_if_changed):
     CloudStorageModuleStub.CheckPermissionLevelForBucket(self, bucket)
     if not remote_path in self.remote_paths[bucket]:
       if only_if_changed:
         return False
       raise CloudStorageModuleStub.NotFoundError('Remote file does not exist.')
     remote_hash = self.remote_paths[bucket][remote_path]
     local_hash = self.local_file_hashes[local_path]
     if only_if_changed and remote_hash == local_hash:
       return False
+    self.downloaded_files.append(remote_path)
     self.local_file_hashes[local_path] = remote_hash
     self.local_hash_files[local_path + '.sha1'] = remote_hash
     return remote_hash
 
   def Get(self, bucket, remote_path, local_path):
     return CloudStorageModuleStub.GetHelper(self, bucket, remote_path,
                                             local_path, False)
 
   def GetIfChanged(self, local_path, bucket=None):
     remote_path = os.path.basename(local_path)
@@ skipping 218 matching lines @@
 class AdbInstallCertStub(object):
   class AndroidCertInstaller(object):
     def __init__(self, device_id, _cert_name, _cert_path):
       if device_id == 'success':
         pass
       elif device_id == 'failure':
         raise Exception('Test exception.')
 
     def install_cert(self, overwrite_cert=False):
       pass