Add percentage of progress in notification header.

ui/strings/ui_strings.grd

Index: ui/strings/ui_strings.grd
diff --git a/ui/strings/ui_strings.grd b/ui/strings/ui_strings.grd
index 7fa2afa0f1e85b75131bbd2f18b756614faba29f..c9af80384b60a6599a82c9c63c1ff7e50da435c8 100644
--- a/ui/strings/ui_strings.grd
+++ b/ui/strings/ui_strings.grd
@@ -634,6 +634,9 @@ need to be translated for each locale.-->
       <message name="IDS_MESSAGE_CENTER_LIST_NOTIFICATION_OVERFLOW_INDICATOR" desc="The overflow indicator shown when a list notification has more list items than visible ones. Should be same as AndroidPlatform msgId 1863231301642314183. (frameworks/base/packages/SystemUI/res/values/strings.xml:notification_group_overflow_indicator)">
         + <ph name="NUMBER">$1<ex>3</ex></ph>
       </message>
+      <message name="IDS_MESSAGE_CENTER_NOTIFICATION_PROGRESS_PERCENTAGE" desc="The summary text in a notification that is shown with progress bar.">
+        <ph name="NUMBER">$1<ex>75</ex></ph> %
+      </message>
       <if expr="not use_titlecase">
         <message name="IDS_MESSAGE_CENTER_QUIET_MODE_BUTTON_TOOLTIP" desc="The tooltip text for the do not disturb button.">
           Do not disturb