Change PageTest.WillStartBrowser to depend on platform instead of browser object as it would not ha…

tools/telemetry/telemetry/page/record_wpr_unittest.py

Index: tools/telemetry/telemetry/page/record_wpr_unittest.py
diff --git a/tools/telemetry/telemetry/page/record_wpr_unittest.py b/tools/telemetry/telemetry/page/record_wpr_unittest.py
index a434fa9622837dd38f4f3f3a1743a36327237598..75e79b2adaa6ccf4d086cf9511ea6a41e9293bb6 100644
--- a/tools/telemetry/telemetry/page/record_wpr_unittest.py
+++ b/tools/telemetry/telemetry/page/record_wpr_unittest.py
@@ -68,7 +68,7 @@ class MockPageTest(page_test.PageTest):
   def ValidatePage(self, page, tab, results):
     self.func_calls.append('ValidatePage')
 
-  def WillStartBrowser(self, browser):
+  def WillStartBrowser(self, platform):
     self.func_calls.append('WillStartBrowser')
 
   def DidStartBrowser(self, browser):
@@ -201,7 +201,7 @@ class RecordWprUnitTests(tab_test_case.TabTestCase):
   def testRecorderPageTest_BrowserMethods(self):
     record_page_test = record_wpr.RecorderPageTest([])
     record_page_test.page_test = MockBenchmark().test()
-    record_page_test.WillStartBrowser(self._tab.browser)
+    record_page_test.WillStartBrowser(self._tab.browser.platform)
     record_page_test.DidStartBrowser(self._tab.browser)
     self.assertTrue('WillStartBrowser' in record_page_test.page_test.func_calls)
     self.assertTrue('DidStartBrowser' in record_page_test.page_test.func_calls)