Add Installer.InstallDateProvisioningSource 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 34974cf587c29f28ada5108773eaba27ac7eaa34..fe527dd5bcae5d379b3ac78f8117dcac5fd3e557 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -6027,6 +6027,15 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Installer.InstallDateProvisioningSource"
+    enum="UpdateEngineInstallDateProvisioningSource">
+  <summary>
+    The source used to provision the install-date-days value sent to Omaha with
+    every request. This is reported when OOBE completes (M34 or later) or when
+    upgrading to a version with install-date-days support.
+  </summary>
+</histogram>
+
 <histogram name="Installer.NormalErrorCodes" enum="UpdateEngineErrorCode">
   <summary>
     Errors from update_engine process when running in normal mode.
@@ -32425,6 +32434,11 @@ other types of suffix sets.
   <int value="42" label="kErrorCodeUpdateCanceledByChannelChange"/>
 </enum>
 
+<enum name="UpdateEngineInstallDateProvisioningSource" type="int">
+  <int value="0" label="Omaha Response"/>
+  <int value="1" label="OOBE Marker"/>
+</enum>
+
 <enum name="UpdateEnginePayloadFormat" type="int">
   <int value="0" label="Full"/>
   <int value="1" label="Delta"/>