Check whether the plugin is disabled in OnIsInternalPluginRegisteredForMimeType().

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 ff0d5af297abfe9c5029141566cec2675f134cfb..e9ffa1c14c851dfa5b0b8da40edce4bb5722c99e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -22041,6 +22041,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>The result from an attempt to load a PPAPI plugin.</summary>
 </histogram>
 
+<histogram name="Plugin.RegistrationStatus.WidevineCdm"
+    enum="PluginRegistratinoStatus">

[ddorwin, 2014/07/18 23:50:18]

Registration

[xhwang, 2014/07/19 00:07:14]

Done.

+  <owner>xhwang@chromium.org</owner>
+  <summary>The registration status of Widevine CDM.</summary>
+</histogram>
+
 <histogram name="Power.BacklightLevelOnAC" units="%">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>
@@ -44501,6 +44507,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="4" label="FILE_MISSING"/>
 </enum>
 
+<enum name="PluginRegistratinoStatus" type="int">
+  <int value="0" label="PLUGIN_REGISTERED"/>
+  <int value="1" label="PLUGIN_NOT_REGISTERED"/>
+  <int value="2" label="PLUGIN_DISABLED"/>
+</enum>
+
 <enum name="PNaClOptionsOptLevelEnum" type="int">
   <int value="0" label="0"/>
   <int value="1" label="1"/>