Fix histograms.xml to follow pretty_print.py results

This malformed summary description causes continuous presubmit
warnings for changes touching tools/metrics.

TBR=isherman@chromium.org

Change-Id: I3b745fb55f108b3a741046ac8809b6f421d15a0f
Reviewed-on: https://chromium-review.googlesource.com/566165Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485546}

tools/metrics/histograms/histograms.xml

@@ -81124,8 +81124,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <owner>sorin@chromium.org</owner>
   <summary>
     True if a new BITS job was created to download the url, or false, if an
-    existing job was found in the BITS queue. The metric is recorded when
-    the component updater background downloader is asked to download a CRX.
+    existing job was found in the BITS queue. The metric is recorded when the
+    component updater background downloader is asked to download a CRX.
   </summary>
 </histogram>