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The following lines are repeated in almost every test cc/scheduler/scheduler_unittest.cc file
  FakeSchedulerClient client;
  SchedulerSettings scheduler_settings;
  scheduler_settings.use_external_begin_frame_source = true;

  CREATE_SCHEDULER_AND_INIT_SURFACE(scheduler_settings);

created test fixture class and clean up to remove duplicate codes.

BUG=449028

Review URL: https://codereview.chromium.org/844763008

Cr-Commit-Position: refs/heads/master@{#313619}