[tools/perf] Reference legacy_page_test module instead of page_test

tools/perf/page_sets/repaint_helpers.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.
 
-from telemetry.page import page_test
+from telemetry.page import legacy_page_test
 
 
 def Repaint(action_runner, mode='viewport', width=None, height=None):
   action_runner.WaitForJavaScriptCondition(
     'document.readyState == "complete"', 90)
   # Rasterize only what's visible.
   action_runner.ExecuteJavaScript(
       'chrome.gpuBenchmarking.setRasterizeOnlyVisibleContent();')
 
   args = {}
@@ skipping 10 matching lines @@
           chrome.gpuBenchmarking.runMicroBenchmark(
               "invalidation_benchmark",
               function(value) {},
               """ + str(args) + """
           );
   """)
 
   micro_benchmark_id = action_runner.EvaluateJavaScript(
       'window.benchmark_results.id')
   if not micro_benchmark_id:
-    raise page_test.MeasurementFailure(
+    raise legacy_page_test.MeasurementFailure(
         'Failed to schedule invalidation_benchmark.')
 
   with action_runner.CreateInteraction('Repaint'):
     action_runner.RepaintContinuously(seconds=5)
 
   action_runner.ExecuteJavaScript("""
       window.benchmark_results.message_handled =
           chrome.gpuBenchmarking.sendMessageToMicroBenchmark(
               """ + str(micro_benchmark_id) + """, {
                 "notify_done": true
               });
   """)