Plugin Power Saver: Add Poster Param metric.

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 4e8128da5b10f95847e2fc6409757a637b13f19b..bd8f0f3d60905f8087f28d1c93b190f3cbb72ef6 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -26739,6 +26739,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Plugin.PowerSaver.PosterParamPresence"
+    enum="PluginPowerSaverPosterParamPresence">
+  <owner>tommycli@chromium.org</owner>
+  <summary>Record how many plugin object tags use poster param.</summary>

[Alexei Svitkine (slow), 2015/02/20 13:54:51]

Nit: Mention when this is recorded. e.g. on every page load? Or, once per plugin
object seen? Or ...?

Also, mention that this is specific to Flash plugins, since that's what the code
appears to be doing.

[tommycli, 2015/02/20 17:20:01]

Done.

+</histogram>
+
 <histogram name="Plugin.PowerSaver.Unthrottle"
     enum="PluginPowerSaverUnthrottleMethod">
   <owner>tommycli@chromium.org</owner>
@@ -55200,6 +55206,13 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="4" label="Essential Cross-Origin Tiny"/>
 </enum>
 
+<enum name="PluginPowerSaverPosterParamPresence" type="int">
+  <int value="0" label="No poster param. Plugin power saver disabled."/>
+  <int value="1" label="No poster param. Plugin power saver enabled."/>
+  <int value="2" label="Poster param exists. Plugin power saver disabled."/>
+  <int value="3" label="Poster param exists. Plugin power saver enabled."/>
+</enum>
+
 <enum name="PluginPowerSaverUnthrottleMethod" type="int">
   <int value="0" label="Never Unthrottled"/>
   <int value="1" label="Unthrottled by Click"/>