Add WebView startup time benchmark

tools/perf/benchmarks/system_health.py

Index: tools/perf/benchmarks/system_health.py
diff --git a/tools/perf/benchmarks/system_health.py b/tools/perf/benchmarks/system_health.py
index 598ff82909401a4a9cc4b2a624cb84567c069a48..4324302a8ed8493a7deb997f3046df38f2745d99 100644
--- a/tools/perf/benchmarks/system_health.py
+++ b/tools/perf/benchmarks/system_health.py
@@ -38,6 +38,7 @@ class SystemHealthTop25(_SystemHealthBenchmark):
   def Name(cls):
     return 'system_health.top25'
 
+
 @benchmark.Disabled('android')  # crbug.com/601953
 @benchmark.Disabled('all')  # crbug.com/613050
 class SystemHealthKeyMobileSites(_SystemHealthBenchmark):
@@ -73,6 +74,27 @@ class _MemorySystemHealthBenchmark(perf_benchmark.PerfBenchmark):
   def Name(cls):
     return 'system_health.memory_%s' % cls.page_set.PLATFORM
 
+@benchmark.Enabled('android')
+class WebviewStartupSystemHealthBenchmark(_SystemHealthBenchmark):
+  """Chrome Webview Startup Time System Health Benchmark.

[charliea (OOO until 10-5), 2016/06/08 20:57:58]

I don't think this first line is useful. I'd prefer just 

"""A benchmark that measures how long it takes WebView to start up and load a
blank page.
"""

[alexandermont, 2016/06/08 21:09:15]

Done

+
+  Benchmark that measures the amount of time that WebView takes
+  to start up and then to load a blank page.
+  """
+  page_set = page_sets.BlankPageSet

[charliea (OOO until 10-5), 2016/06/08 20:57:58]

nit: can you add a blank line between this line and the next?

[alexandermont, 2016/06/08 21:09:15]

Done

+  def CreateTimelineBasedMeasurementOptions(self):
+    options = timeline_based_measurement.Options(

[charliea (OOO until 10-5), 2016/06/08 20:57:58]

nit: this can be deleted (it's the default)

[alexandermont, 2016/06/08 21:09:15]

Done

+        tracing_category_filter.TracingCategoryFilter())
+    options.SetTimelineBasedMetric('webviewStartupMetric')
+    options.config.enable_atrace_trace = True
+    options.config.enable_chrome_trace = False

[charliea (OOO until 10-5), 2016/06/08 20:57:58]

nit: this can be deleted (it's the default)

[alexandermont, 2016/06/08 21:09:15]

Done

+    options.config.atrace_config.app_name = 'org.chromium.webview_shell'
+    return options
+
+  @classmethod
+  def Name(cls):
+    return 'system_health.webview_startup'
+
 # https://github.com/catapult-project/catapult/issues/2340
 @benchmark.Disabled('all')
 class DesktopMemorySystemHealth(_MemorySystemHealthBenchmark):