Mark IncognitoModePrefs.WindowsParentalControlsInit* Obsolete

This histogram was removed in http://crrev.com/747875.

Fixed: 975109
Change-Id: I8dcfafa5b950b10245910f92e6805d06e8a28bf8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3070018
Auto-Submit: Robert Liao <robliao@chromium.org>
Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
Cr-Commit-Position: refs/heads/master@{#908877}
diff --git a/tools/metrics/histograms/metadata/others/histograms.xml b/tools/metrics/histograms/metadata/others/histograms.xml
index d86c858..358e70a 100644
--- a/tools/metrics/histograms/metadata/others/histograms.xml
+++ b/tools/metrics/histograms/metadata/others/histograms.xml
@@ -7937,6 +7937,9 @@
 
 <histogram name="IncognitoModePrefs.WindowsParentalControlsInitThread"
     enum="ThreadType" expires_after="M77">
+  <obsolete>
+    Removed in http://crrev.com/747875.
+  </obsolete>
   <owner>robliao@chromium.org</owner>
   <summary>
     The thread used to initialize the Windows parental controls.
@@ -7945,6 +7948,9 @@
 
 <histogram name="IncognitoModePrefs.WindowsParentalControlsInitTime" units="ms"
     expires_after="M77">
+  <obsolete>
+    Removed in http://crrev.com/747875.
+  </obsolete>
   <owner>robliao@chromium.org</owner>
   <summary>
     The amount of time that elapsed during a run of