[Extensions] Extend ExtensionUrlRequest.* UMAs' expiry.

These are used to monitor extension resource request read stats, hence
extend these by one more year.

Following three UMAs were change in this CL:
ExtensionUrlRequest.Latency
                   .SeekPosition
                   .TotalKbRead

Bug: 1016408
Change-Id: I61246cb38003e5cffab20fb9366477c10cd9a01c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1873086Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708419}

tools/metrics/histograms/histograms.xml

@@ -47702,7 +47702,7 @@ uploading your change for review.
 </histogram>
 
 <histogram name="ExtensionUrlRequest.Latency" units="ms"
-    expires_after="2019-11-30">
+    expires_after="2020-11-30">
   <owner>lazyboy@chromium.org</owner>
   <summary>The time taken to complete an extension url request.</summary>
 </histogram>
@@ -47737,7 +47737,7 @@ uploading your change for review.
 </histogram>
 
 <histogram name="ExtensionUrlRequest.SeekPosition" units="units"
-    expires_after="2019-11-30">
+    expires_after="2020-11-30">
   <owner>lazyboy@chromium.org</owner>
   <summary>
     When fetching a chrome-extension:// URL, this indicates the first byte
@@ -47749,7 +47749,7 @@ uploading your change for review.
 </histogram>
 
 <histogram name="ExtensionUrlRequest.TotalKbRead" units="KB"
-    expires_after="2019-11-30">
+    expires_after="2020-11-30">
   <owner>lazyboy@chromium.org</owner>
   <summary>
     The total number of bytes read for a chrome-extension:// URL, logged when