Make credential_path a page attribute instead of page_set attribute.

tools/telemetry/telemetry/page/page_runner_unittest.py

 # Copyright 2014 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 os
 import tempfile
 import unittest
 
 from telemetry import benchmark
@@ skipping 311 matching lines @@
   def testCredentialsWhenLoginSucceeds(self):
     credentials_backend = StubCredentialsBackend(login_return_value=True)
     did_run = self.runCredentialsTest(credentials_backend)
     assert credentials_backend.did_get_login == True
     assert credentials_backend.did_get_login_no_longer_needed == True
     assert did_run
 
   def runCredentialsTest(self, credentials_backend):
     ps = page_set.PageSet()
     expectations = test_expectations.TestExpectations()
-    page = page_module.Page(
-        'file://blank.html', ps, base_dir=util.GetUnittestDataDir())
-    page.credentials = "test"
-    ps.pages.append(page)
-
     did_run = [False]
 
     try:
       with tempfile.NamedTemporaryFile(delete=False) as f:
+        page = page_module.Page(
+        'file://blank.html', ps, base_dir=util.GetUnittestDataDir(),
+        credentials_path=f.name)
+        page.credentials = "test"
+        ps.pages.append(page)
+
         f.write(SIMPLE_CREDENTIALS_STRING)
-        ps.credentials_path = f.name
 
       class TestThatInstallsCredentialsBackend(page_test.PageTest):
         def __init__(self, credentials_backend):
           super(TestThatInstallsCredentialsBackend, self).__init__()
           self._credentials_backend = credentials_backend
 
         def DidStartBrowser(self, browser):
           browser.credentials.AddBackend(self._credentials_backend)
 
         def ValidatePage(self, *_):
@@ skipping 300 matching lines @@
       if ii <= expected_max_failures:
         self.assertTrue(ps.pages[ii].was_run)
       else:
         self.assertFalse(ps.pages[ii].was_run)
 
   def testMaxFailuresOptionIsRespected(self):
     self._testMaxFailuresOptionIsRespectedAndOverridable()
 
   def testMaxFailuresOptionIsOverridable(self):
     self._testMaxFailuresOptionIsRespectedAndOverridable(1)