Replace eugenebut with ajuma for some histogram owners

Bug: None
Change-Id: If9375f350e354325a6eccd56ab47ace3d3c7130a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2642755Reviewed-by: Ali Juma <ajuma@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846308}

tools/metrics/histograms/histograms_xml/ios/histograms.xml

@@ -818,16 +818,16 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="IOS.Snapshots.CacheSize" units="KB" expires_after="2021-07-11">
+  <owner>ajuma@chromium.org</owner>
   <owner>edchin@chromium.org</owner>
-  <owner>eugenebut@chromium.org</owner>
   <summary>
     The overall size of snapshots cache. Recorded when new snapshot is cached.
   </summary>
 </histogram>
 
 <histogram name="IOS.Snapshots.ImageSize" units="KB" expires_after="2021-07-11">
+  <owner>ajuma@chromium.org</owner>
   <owner>edchin@chromium.org</owner>
-  <owner>eugenebut@chromium.org</owner>
   <summary>
     The size of a single snapshot image. Recorded when new snapshot is taken and
     RecordSnapshotSize flag is enabled.
@@ -835,8 +835,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="IOS.Snapshots.PDFSize" units="KB" expires_after="2021-07-11">
+  <owner>ajuma@chromium.org</owner>
   <owner>edchin@chromium.org</owner>
-  <owner>eugenebut@chromium.org</owner>
   <summary>
     The size of a single snapshot PDF. Recorded when new snapshot is taken and
     RecordSnapshotSize flag is enabled.

tools/metrics/histograms/histograms_xml/memory/histograms.xml

@@ -284,8 +284,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="Memory.Browser.MemoryFootprint.NumLiveOverscroll" units="tabs"
     expires_after="2021-07-11">
+  <owner>ajuma@chromium.org</owner>
   <owner>rkgibson@google.com</owner>
-  <owner>eugenebut@chromium.org</owner>
   <summary>
     Investigation into crbug.com/1102494 shows that OverscrollActionsController
     is allocating thousands of objects in it's -initWithScrollView:. This is
@@ -299,8 +299,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="Memory.Browser.MemoryFootprint.NumOpenTabs" units="tabs"
     expires_after="2021-07-11">
+  <owner>ajuma@chromium.org</owner>
   <owner>rkgibson@google.com</owner>
-  <owner>eugenebut@chromium.org</owner>
   <summary>
     Investigation into crbug.com/1102494 shows that OverscrollActionsController
     is allocating thousands of objects in it's -initWithScrollView:. This is