[Telemetry] Re-add API to tear down state after each story run

telemetry/telemetry/benchmark.py

Index: telemetry/telemetry/benchmark.py
diff --git a/telemetry/telemetry/benchmark.py b/telemetry/telemetry/benchmark.py
index 74febf1ea94c862bc2e77d06fbe68aa6dcddc0d7..44511e76a1147e5ade4991623efaa25ff8018c5c 100644
--- a/telemetry/telemetry/benchmark.py
+++ b/telemetry/telemetry/benchmark.py
@@ -99,6 +99,20 @@ class Benchmark(command_line.Command):
     return '%s.%s' % (cls.__module__.split('.')[-1], cls.__name__)
 
   @classmethod
+  def ShouldTearDownStateAfterEachStoryRun(cls):
+    """Override this method to tear down state after each story run.
+
+    Tearing down all states after each story run, e.g., clearing profiles,
+    stopping the browser, stopping local server, etc. So the browser will not be
+    reused among multiple stories. This is particularly useful to get the
+    startup part of launching the browser in each story.
+
+    This should only be used by TimelineBasedMeasurement (TBM) benchmarks, but
+    not by PageTest based benchmarks.
+    """
+    return False
+
+  @classmethod
   def AddCommandLineArgs(cls, parser):
     group = optparse.OptionGroup(parser, '%s test options' % cls.Name())
     cls.AddBenchmarkCommandLineArgs(group)