Extend expiry of SBClientDownload.DownloadRequestNetError

This metric is expected to be generally useful in case of any debugging
reliability with Safe Browsing's download protection endpoint. We have a
Chirp elert on SBClientDownload.CheckDownloadStats, and any rise in the
SERVER_PING_FAILED bucket would cause us to check this metric.

Fixed: 1153861
Change-Id: I82cd811869549976c9eef5358c0a41e37b9d7db1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2577486
Auto-Submit: Daniel Rubery <drubery@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834563}

tools/metrics/histograms/histograms_xml/sb_client/histograms.xml

@@ -105,8 +105,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="SBClientDownload.DownloadRequestNetError" enum="NetErrorCodes"
-    expires_after="2021-01-10">
-  <owner>vakh@chromium.org</owner>
+    expires_after="2021-07-10">
+  <owner>drubery@chromium.org</owner>
   <owner>chrome-safebrowsing-alerts@google.com</owner>
   <owner>mattm@chromium.org</owner>
   <summary>