https://chromium-review.googlesource.com/c/chromium/src/+/869890 updated an i18n message to be plural 

chrome/app/md_extensions_strings.grdp
 string IDS_MD_EXTENSIONS_ERROR_LINES_NOT_SHOWN
   "other {<$1 lines not shown>}}"

Placeholder elements like $1 $2, should be wrapped in <ph> elements according to the docs [1] [2]

[1] https://sites.google.com/a/chromium.org/dev/developers/design-documents/ui-localization#TOC-How-to-add-a-string
[2] https://sites.google.com/a/chromium.org/dev/developers/tools-we-use-in-chromium/grit/grit-users-guide#Adding_Resources

but the docs do not mention how/what to do with plurals.  Should placeholder $1 $2 etc in plurals be wrapped in <ph> elements?

I noticed that components/payments_strings.grdp

  <message name="IDS_PAYMENT_REQUEST_ORDER_SUMMARY_MORE_ITEMS" desc="The label in the Order Summary section of the Payment Sheet that indicates how many display items are hidden. [ICU Syntax]">
    {MORE_ITEMS, plural,
      =1 {<ph name="ITEM_COUNT">#<ex>1</ex></ph> more item}
      other {<ph name="ITEM_COUNT">#<ex>2</ex></ph> more items}}
  </message>

wrapped them.  I also noticed how a translated plural message that did not wrap its placesholders $1 $2 $3, appeared (badly) in language=bn 

./components/strings/components_strings_bn.xtb
<translation id="262424810616849754">{COUNT,plural, =0{কিছুই নয়}=1{১টি অ্যাপ ($১)}=2{২টি অ্যাপ ($১, $২)}one{#টি অ্যাপ ($১, $২, $৩)}other{#টি অ্যাপ ($১, $২, $৩)}}</translation>

Suggests to me that placeholders in plurals should be wrapped in <ph>.  Thoughts?