[Telemetry] Add StoryExpectations to loading.desktop; disabling uol.com story on linux

Requires https://codereview.chromium.org/2887983003/ to land first

BUG=723783

Review-Url: https://codereview.chromium.org/2885203003
Cr-Commit-Position: refs/heads/master@{#473419}

tools/perf/benchmarks/loading.py

@@ -37,6 +37,9 @@ class LoadingDesktop(_LoadingBase):
         cache_temperatures=[cache_temperature.PCV1_COLD,
                             cache_temperature.PCV1_WARM,])
 
+  def GetExpectations(self):
+    return page_sets.LoadingDesktopExpectations()
+
   @classmethod
   def Name(cls):
     return 'loading.desktop'

tools/perf/page_sets/__init__.py

@@ -13,8 +13,9 @@ from telemetry import story
 # Import all submodules' PageSet classes.
 start_dir = os.path.dirname(os.path.abspath(__file__))
 top_level_dir = os.path.dirname(start_dir)
-base_class = story.StorySet
+base_classes = [story.StorySet, story.expectations.StoryExpectations]
 
-for cls in discover.DiscoverClasses(
-    start_dir, top_level_dir, base_class).values():
-  setattr(sys.modules[__name__], cls.__name__, cls)
+for base_class in base_classes:
+  for cls in discover.DiscoverClasses(
+      start_dir, top_level_dir, base_class).values():
+    setattr(sys.modules[__name__], cls.__name__, cls)

tools/perf/page_sets/loading_desktop.py

@@ -108,3 +108,9 @@ class LoadingDesktopStorySet(story.StorySet):
           self.AddStory(page_cycler_story.PageCyclerStory(url, self,
               shared_page_state_class=shared_page_state.SharedMobilePageState,
               cache_temperature=temp, tags=tags, name=name))
+
+
+class LoadingDesktopExpectations(story.expectations.StoryExpectations):
+  def SetExpectations(self):
+    self.DisableStory(
+        'uol.com.br', [story.expectations.ALL_LINUX], 'crbug.com/723783')