[tools/perf] Create a list of tags for system_health_story

tools/perf/page_sets/system_health/system_health_story.py

Index: tools/perf/page_sets/system_health/system_health_story.py
diff --git a/tools/perf/page_sets/system_health/system_health_story.py b/tools/perf/page_sets/system_health/system_health_story.py
index 78b9347b73e0787a72ea31f5d76a5c6da5243b1c..72afe472fc3349707e4c96a7c9c594e7c9c0325c 100644
--- a/tools/perf/page_sets/system_health/system_health_story.py
+++ b/tools/perf/page_sets/system_health/system_health_story.py
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 from page_sets.system_health import platforms
+from page_sets.system_health import system_health_tags
 
 from telemetry import decorators
 from telemetry.page import page
@@ -65,12 +66,18 @@ class SystemHealthStory(page.Page):
   URL = NotImplemented
   ABSTRACT_STORY = True
   SUPPORTED_PLATFORMS = platforms.ALL_PLATFORMS
+  TAGS = None
 
   def __init__(self, story_set, take_memory_measurement):
     case, group, _ = self.NAME.split(':')
+    tags = []

[charliea (OOO until 10-5), 2017/01/24 23:00:05]

Why build up tags? Can't we just pass in self.TAGS after validating that they
all belong to ALL_TAGS?

[nednguyen, 2017/02/03 15:02:42]

Actually the TAG_INFOS, not TAGS, so people can write:

TAG_INFOS = [story_tags.AUDIO_PLAYING, story_tags.CSS_ANIMATION]

+    if self.TAGS:
+      for t in self.TAGS:
+        assert t in system_health_tags.ALL_TAGS
+        tags.append(t)

[perezju, 2017/01/24 19:50:05]

High level question, as a benchmark writer you expect clients to write e.g.:

    class MyNewFunStory(system_health_story.SystemHealthStory):
        TAGS = ['audio-playing', 'css-animation']
        ...

And then this bit of code here just checks that the tags provided (as strings)
are valid?

If that is the case (and I think that's a good interface), maybe just expose a
system_health_tags.ValidateTags() method?

No need to define a TagInfo class at all, a simple private dict mapping tags to
their descriptions should be enough. What do you think?

[nednguyen, 2017/02/03 15:02:42]

I expect clients to write: 
TAGS = [story_tags.AUDIO_PLAYING, story_tags.CSS_ANIMATION]

Using a dict as you proposed make it a bit clumsy for ensuring documentation for
each extra tag, i.e:

TAG_A = '...'
TAG_B = '...'

....

description = {
TAG_A: '...',  # <- adding another tag require adding code in two separate place
TAG_B: '...',
...
}

[perezju, 2017/02/03 15:52:21]

Acknowledged. If you wan't to define (and use) the constant names then a
dictionary doesn't make sense.

     super(SystemHealthStory, self).__init__(
         shared_page_state_class=_SystemHealthSharedState, page_set=story_set,
-        name=self.NAME, url=self.URL,
+        name=self.NAME, url=self.URL, tags=tags,
         credentials_path='../data/credentials.json',
         grouping_keys={'case': case, 'group': group})
     self._take_memory_measurement = take_memory_measurement