[system-health] Add support for disabling individual stories on individual platforms

tools/perf/page_sets/system_health/system_health_story.py

 # Copyright 2016 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 page_sets.system_health import platforms
 
+from telemetry import decorators
 from telemetry.page import page
+from telemetry.page import shared_page_state
 
 
 # Extra wait time after the page has loaded required by the loading metric. We
 # use it in all benchmarks to avoid divergence between benchmarks.
 # TODO(petrcermak): Switch the memory benchmarks to use it as well.
 _WAIT_TIME_AFTER_LOAD = 10
 
 
+class _SystemHealthSharedState(shared_page_state.SharedPageState):
+  """Shared state which enables disabling stories on individual platforms.
+
+  This class adds support for enabling/disabling individual stories on
+  individual platforms using the same approaches as for benchmarks:
+
+    1. Disabled/Enabled decorator:
+
+       @decorators.Disabled('win')
+       class Story(system_health_story.SystemHealthStory):
+         ...
+
+    2. ShouldDisable method:
+
+       class Story(system_health_story.SystemHealthStory):
+         ...
+
+         @classmethod
+         def ShouldDisable(cls, possible_browser):
+           return possible_browser.platform.GetOSName() == 'win'
+  """
+
+  def CanRunStory(self, story):
+    return story.CanRun(self.possible_browser)
+
+
 class _MetaSystemHealthStory(type):
   """Metaclass for SystemHealthStory."""
 
   @property
   def ABSTRACT_STORY(cls):
     """Class field marking whether the class is abstract.
 
     If true, the story will NOT be instantiated and added to a System Health
     story set. This field is NOT inherited by subclasses (that's why it's
     defined on the metaclass).
     """
     return cls.__dict__.get('ABSTRACT_STORY', False)
 
 
 class SystemHealthStory(page.Page):
   """Abstract base class for System Health user stories."""
   __metaclass__ = _MetaSystemHealthStory
 
   # The full name of a single page story has the form CASE:GROUP:PAGE (e.g.
   # 'load:search:google').
   NAME = NotImplemented
   URL = NotImplemented
   ABSTRACT_STORY = True
   SUPPORTED_PLATFORMS = platforms.ALL_PLATFORMS
 
   def __init__(self, story_set, take_memory_measurement):
     case, group, _ = self.NAME.split(':')
     super(SystemHealthStory, self).__init__(
-        page_set=story_set, name=self.NAME, url=self.URL,
+        shared_page_state_class=_SystemHealthSharedState, page_set=story_set,
+        name=self.NAME, url=self.URL,
         credentials_path='../data/credentials.json',
         grouping_keys={'case': case, 'group': group})
     self._take_memory_measurement = take_memory_measurement
 
+  @classmethod
+  def CanRun(cls, possible_browser):
+    if (decorators.ShouldSkip(cls, possible_browser)[0] or
+        cls.ShouldDisable(possible_browser)):
+      return False
+    return True
+
+  @classmethod
+  def ShouldDisable(cls, possible_browser):
+    """Override this method to disable a story under specific conditions.
+
+    This method is modelled after telemetry.benchmark.Benchmark.ShouldDisable().
+    """
+    del possible_browser
+    return False
+
   def _Measure(self, action_runner):
     if self._take_memory_measurement:
       action_runner.MeasureMemory(deterministic_mode=True)
     else:
       action_runner.Wait(_WAIT_TIME_AFTER_LOAD)
 
   def _Login(self, action_runner):
     pass
 
   def _DidLoadDocument(self, action_runner):
     pass
 
   def RunNavigateSteps(self, action_runner):
     self._Login(action_runner)
     super(SystemHealthStory, self).RunNavigateSteps(action_runner)
 
   def RunPageInteractions(self, action_runner):
     action_runner.tab.WaitForDocumentReadyStateToBeComplete()
     self._DidLoadDocument(action_runner)
     self._Measure(action_runner)