Re-enable memory.top_7_stress test now that bug 455349 is fixed.

tools/perf/benchmarks/memory.py

 # Copyright 2013 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 measurements import memory
 import page_sets
 from telemetry import benchmark
 
 
 @benchmark.Enabled('android')
 class MemoryMobile(benchmark.Benchmark):
   test = memory.Memory
   page_set = page_sets.MobileMemoryPageSet
 
   @classmethod
   def Name(cls):
     return 'memory.mobile_memory'
 
 
-@benchmark.Disabled  # http://crbug.com/459646
 class MemoryTop7Stress(benchmark.Benchmark):
   """Use (recorded) real world web sites and measure memory consumption."""
   test = memory.Memory
   page_set = page_sets.Top7StressPageSet
 
   @classmethod
   def Name(cls):
     return 'memory.top_7_stress'