Add WebView Multiprocess startup benchmark.

tools/perf/page_sets/system_health/blank_stories.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 system_health_story
+
+
+class _BlankStory(system_health_story.SystemHealthStory):

[petrcermak, 2016/09/08 11:33:17]

There's no point in splitting the story into two classes. You can just define
BlankAboutBlankStory straightaway.

[mikecase (-- gone --), 2016/09/08 16:51:49]

Done

+  """Abstract base class for blank page stories."""
+  ABSTRACT_STORY = True
+
+  def _DidLoadDocument(self, action_runner):
+    # Request a RAF and wait for it to be processed to ensure that the metric

[petrcermak, 2016/09/08 11:33:17]

I don't think you need this. The stories wait for 10 seconds if there's no
memory measurement and 6 seconds if there are memory measurements. If there
hasn't been a RAF for more than 5 seconds, then I think we're really screwed
anyway.

[mikecase (-- gone --), 2016/09/08 16:51:49]

Ack

+    # Startup.FirstWebContents.NonEmptyPaint2 is recorded.
+    action_runner.ExecuteJavaScript(
+        """

[petrcermak, 2016/09/08 11:33:17]

If you do want to keep this code, than:

* s/hasRunRAF/__hasRunRAF/g
* s/this/window/g
* s/==/===/g
* s/0/false/g and s/1/true/g
* indent only 2 spaces on line 19

[mikecase (-- gone --), 2016/09/08 16:51:49]

Done, Done, Done, Done, Done

+        this.hasRunRAF = 0;
+        requestAnimationFrame(function() {
+            this.hasRunRAF = 1;
+        });
+        """
+    )
+    action_runner.WaitForJavaScriptCondition("this.hasRunRAF == 1")
+
+
+class BlankStoryAboutBlank(_BlankStory):

[petrcermak, 2016/09/08 11:33:17]

nit: BlankAboutBlankStory (the last word should be "Story")

[mikecase (-- gone --), 2016/09/08 16:51:49]

Done

+  NAME = 'blank:about:blank'
+  URL = 'about:blank'