[LazyParseCSS] Add metrics for total # of rules at 0% and 100% usage

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index aa69c7280c4795c21f5ecb118515c7aa99222e1e..84b91ce94095232f2b8c1c3925098470ed1a61f5 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -66527,6 +66527,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Style.TotalLazyRules" units="count">
+  <owner>csharrison@chromium.org</owner>
+  <summary>
+    Tracks the total number of rules that have parsing lazily deferred in an
+    author style sheet.
+  </summary>
+</histogram>
+
+<histogram name="Style.TotalLazyRules.FullUsage" units="count">

[jwd, 2017/02/14 15:57:05]

Not important now, but this could have been defined using the suffixes mechanism
described at the top of this file. No need to change it, but if you ever add
more TotalLazyRules.* histograms, I recommend you switch to that.

+  <owner>csharrison@chromium.org</owner>
+  <summary>
+    Tracks the total number of rules that have parsing lazily deferred in an
+    author style sheet, for sheets that ended up needing all their rules.
+  </summary>
+</histogram>
+
 <histogram name="Style.UpdateTime" units="microseconds">
   <owner>csharrison@chromium.org</owner>
   <summary>Microseconds spent in Document::updateStyle.</summary>