[Telemetry] Explicitly define Name() method for all perf benchmarks

tools/perf/benchmarks/task_execution_time.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.
 
 import page_sets
 from measurements import task_execution_time
 from telemetry import benchmark
 
 
 @benchmark.Enabled('android')
 class TaskExecutionTimeKeyMobileSites(benchmark.Benchmark):
   """Measures task execution statistics while scrolling down key mobile sites.
   http://www.chromium.org/developers/design-documents/rendering-benchmarks"""
   test = task_execution_time.TaskExecutionTime
   page_set = page_sets.KeyMobileSitesSmoothPageSet
 
+  @classmethod
+  def Name(cls):
+    return 'task_execution_time.key_mobile_sites_smooth'
+
 
 @benchmark.Enabled('android')
 class TaskExecutionTimeToughSchedulingCases(benchmark.Benchmark):
   """Measures task execution statistics while scrolling tough scheduling sites.
   http://www.chromium.org/developers/design-documents/rendering-benchmarks"""
   test = task_execution_time.TaskExecutionTime
   page_set = page_sets.ToughSchedulingCasesPageSet
+  @classmethod
+  def Name(cls):
+    return 'task_execution_time.tough_scheduling_cases'
+