[Files App] Add observed enumeration value for CrosDisks.Fuse.Rar2fs

BUG=chromium:1058685

Change-Id: Ifa778623b50c373ac179e6e440f68f89d6b23abf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2148981Reviewed-by: Sergei Datsenko <dats@chromium.org>
Commit-Queue: François Degros <fdegros@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759250}

tools/metrics/histograms/enums.xml

@@ -55738,6 +55738,7 @@ https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_2.7.1.pdf
   <int value="1" label="Missing primary volume">Hardcoded in rar2fs</int>
   <int value="13" label="Bad archive">ERAR_BAD_ARCHIVE from libunrar</int>
   <int value="14" label="Unknown format">ERAR_UNKNOWN_FORMAT from libunrar</int>
+  <int value="18" label="Cannot read">ERAR_EREAD from libunrar</int>
   <int value="22" label="Missing password">
     ERAR_MISSING_PASSWORD from libunrar
   </int>