Add support for Command key for Extension Commands

ui/base/strings/ui_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- This file contains definitions of resources that will be translated for
 each locale. Specifically, these are UI strings that are used by app/ that
 need to be translated for each locale.-->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
       source_lang_id="en" enc_check="möl">
   <outputs>
     <!-- TODO add each of your output files.  Modify the three below, and add
@@ skipping 342 matching lines @@
       <!-- Shortcut Modifiers -->
       <message name="IDS_APP_CONTROL_MODIFIER" desc="Control key shortcut modifier">
         Ctrl+<ph name="KEY_COMBO_NAME">$1<ex>C</ex></ph>
       </message>
       <message name="IDS_APP_ALT_MODIFIER" desc="Alt key shortcut modifier">
         Alt+<ph name="KEY_COMBO_NAME">$1<ex>C</ex></ph>
       </message>
       <message name="IDS_APP_SHIFT_MODIFIER" desc="Shift key shortcut modifier">
         Shift+<ph name="KEY_COMBO_NAME">$1<ex>C</ex></ph>
       </message>
+      <message name="IDS_APP_COMMAND_MODIFIER" desc="Command key shortcut modifier">
+        Command+<ph name="KEY_COMBO_NAME">$1<ex>C</ex></ph>
+      </message>
 
       <!-- Byte size units -->
       <message name="IDS_APP_BYTES" desc="Units tag indicating a quantity of bytes">
         <ph name="QUANTITY">$1<ex>42</ex></ph> B
       </message>
       <message name="IDS_APP_KIBIBYTES" desc="Units tag indicating a quantity of kilobytes">
         <ph name="QUANTITY">$1<ex>42.0</ex></ph> KB
       </message>
       <message name="IDS_APP_MEBIBYTES" desc="Units tag indicating a quantity of megabytes">
         <ph name="QUANTITY">$1<ex>42.0</ex></ph> MB
@@ skipping 21 matching lines @@
       </message>
       <message name="IDS_APP_TEBIBYTES_PER_SECOND" desc="Units tag indicating a speed of terabytes/second">
         <ph name="QUANTITY">$1<ex>42.0</ex></ph> TB/s
       </message>
       <message name="IDS_APP_PEBIBYTES_PER_SECOND" desc="Units tag indicating a speed of petabytes/second">
         <ph name="QUANTITY">$1<ex>42.0</ex></ph> PB/s
       </message>
     </messages>
   </release>
 </grit>