Set an expiry date for unused histograms (Conflicts.*, ThirdPartyModules.*)

These are histograms that have not been viewed in the last 6 months, but still
report data on the Stable channel. Set these histograms to stop being recorded
for Chrome releases after 2018-08-30. We will file bugs via Monorail (crbug)
reminding owners about the approaching histogram expiry – initially 30 days
prior to expiry, and also with follow-up alerts. The metrics dashboards will
also display a warning for anyone viewing a soon-to-expire histogram.

Owners and/or users of these histograms: Please comment on this CL if you think
that any affected histogram should not have an expiry date set! This should be
uncommon.

Otherwise, there are a few options going forward:
  * If the histogram is no longer needed, please send a follow-up CL to delete
    the recording code and to mark the histogram as <obsolete>. (You can also
    remove the expiry date in the same CL.)
  * If you want to set a different expiry date, please send a follow-up CL to do
    so.
  * If neither of the above apply, then keep an eye out for Monorail bugs as the
    histogram expiry date approaches.
For more info on how unused histograms are identified, see
https://goto.google.com/uma-unused-histograms-cleanup

Bug: 850539

Change-Id: I6915b08846dd50f587dded3544b990334615d4bc
Reviewed-on: https://chromium-review.googlesource.com/1111597Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Commit-Queue: Gayane Petrosyan <gayane@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585109}

tools/metrics/histograms/histograms.xml

@@ -13640,14 +13640,16 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Conflicts.ConfirmedBadModules" units="modules">
+<histogram name="Conflicts.ConfirmedBadModules" units="modules"
+    expires_after="2018-08-30">
   <owner>chrisha@chromium.org</owner>
   <summary>
     The number of confirmed bad modules found during module enumeration.
   </summary>
 </histogram>
 
-<histogram name="Conflicts.EnumerateLoadedModules" units="ms">
+<histogram name="Conflicts.EnumerateLoadedModules" units="ms"
+    expires_after="2018-08-30">
   <owner>chrisha@chromium.org</owner>
   <summary>
     The length of time it takes to enumerate the loaded modules in the browser
@@ -13655,21 +13657,24 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Conflicts.EnumerateShellExtensions" units="ms">
+<histogram name="Conflicts.EnumerateShellExtensions" units="ms"
+    expires_after="2018-08-30">
   <owner>chrisha@chromium.org</owner>
   <summary>
     The length of time it takes to enumerate the shell extensions.
   </summary>
 </histogram>
 
-<histogram name="Conflicts.EnumerateWinsockModules" units="ms">
+<histogram name="Conflicts.EnumerateWinsockModules" units="ms"
+    expires_after="2018-08-30">
   <owner>chrisha@chromium.org</owner>
   <summary>
     The length of time it takes to enumerate the Winsock LSP modules.
   </summary>
 </histogram>
 
-<histogram name="Conflicts.EnumerationInspectionTime" units="ms">
+<histogram name="Conflicts.EnumerationInspectionTime" units="ms"
+    expires_after="2018-08-30">
   <owner>chrisha@chromium.org</owner>
   <summary>
     The cumulative length of time it takes to inspect all modules on disk,
@@ -13678,7 +13683,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Conflicts.EnumerationTotalTime" units="ms">
+<histogram name="Conflicts.EnumerationTotalTime" units="ms"
+    expires_after="2018-08-30">
   <owner>chrisha@chromium.org</owner>
   <summary>
     The cumulative length of time it takes to enumerate and inspect all modules.
@@ -13687,7 +13693,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Conflicts.SuspectedBadModules" units="modules">
+<histogram name="Conflicts.SuspectedBadModules" units="modules"
+    expires_after="2018-08-30">
   <owner>chrisha@chromium.org</owner>
   <summary>
     The number of suspected bad modules found during module enumeration.
@@ -105620,7 +105627,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="ThirdPartyModules.Certificates.Total" units="certificates">
+<histogram name="ThirdPartyModules.Certificates.Total" units="certificates"
+    expires_after="2019-12-31">
   <owner>chrisha@chromium.org</owner>
   <summary>
     The total number of certificates for modules loaded (or potentially loaded)
@@ -105693,7 +105701,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="ThirdPartyModules.Modules.NotLoaded" units="modules">
+<histogram name="ThirdPartyModules.Modules.NotLoaded" units="modules"
+    expires_after="2019-12-31">
   <owner>chrisha@chromium.org</owner>
   <summary>
     The total number of third-party modules (neither Microsoft nor Google) that
@@ -105702,7 +105711,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="ThirdPartyModules.Modules.Signed" units="modules">
+<histogram name="ThirdPartyModules.Modules.Signed" units="modules"
+    expires_after="2019-12-31">
   <owner>chrisha@chromium.org</owner>
   <summary>
     The total number of signed modules loaded (or potentially loaded) into the
@@ -105710,7 +105720,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="ThirdPartyModules.Modules.Signed.Catalog" units="modules">
+<histogram name="ThirdPartyModules.Modules.Signed.Catalog" units="modules"
+    expires_after="2019-12-31">
   <owner>chrisha@chromium.org</owner>
   <summary>
     The total number of modules loaded (or potentially loaded) into the browser