function installMockClock() {
  clock.install();

  // Overwrite the "protected" setTimeout and clearTimeout with the versions
  // replaced by MockClock. Normal tests should never do this, but we need to
  // test the ContinuationTest itself.
  stubs.set(
      ContinuationTestCase.Step, 'protectedClearTimeout_', window.clearTimeout);
  stubs.set(
      ContinuationTestCase.Step, 'protectedSetTimeout_', window.setTimeout);
}
Installs the Mock Clock and replaces the Step timeouts with the mock
implementations.