change units to ms for MPArch.ChildProcessLaunch

Change units to ms for MPArch.ChildProcessLaunch, also update owners.

Bug: None
Change-Id: I09ab0ea5aaf10a0ae62a508daeb868787dad4ee1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3218080
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Commit-Queue: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/main@{#931015}

tools/metrics/histograms/metadata/others/histograms.xml

@@ -11087,18 +11087,20 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <summary>Mouse scroll sensitivity value. Only reported on Chrome OS.</summary>
 </histogram>
 
-<histogram name="MPArch.ChildProcessLaunchFirst" units="units"
+<histogram name="MPArch.ChildProcessLaunchFirst" units="ms"
     expires_after="2022-05-01">
-  <owner>ppi@chromium.org</owner>
+  <owner>pasko@chromium.org</owner>
+  <owner>yfriedman@chromium.org</owner>
   <summary>
     The time it takes to spawn the first child subprocess (including sandbox
     init).
   </summary>
 </histogram>
 
-<histogram name="MPArch.ChildProcessLaunchSubsequent" units="units"
+<histogram name="MPArch.ChildProcessLaunchSubsequent" units="ms"
     expires_after="2022-04-24">
-  <owner>ppi@chromium.org</owner>
+  <owner>pasko@chromium.org</owner>
+  <owner>yfriedman@chromium.org</owner>
   <summary>
     The time it takes to spawn child sub processes not counting the first one.
   </summary>