Update external protocol handler strings to use "can't" instead of "cannot".

chrome/app/chromium_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 <!-- This file contains definitions of strings that are distribution specific.
 If you update this file, be sure also to update google_chrome_strings.grd. -->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
       output_all_resource_defines="false" source_lang_id="en" enc_check="möl">
   <outputs>
     <output filename="grit/chromium_strings.h" type="rc_header">
       <emit emit_type='prepend'></emit>
     </output>
@@ skipping 303 matching lines @@
         </message>
       </if>
       <if expr="not chromeos and not is_ios">
         <message name="IDS_NEW_TAB_CHROME_WELCOME_PAGE_TITLE"
                  desc="Title for the hard-coded thumbnail that represents the Google Chrome Welcome page.  This is used on the NTP when there aren't enough thumbnails to show.">
           Welcome to Chromium
         </message>
       </if>
       <if expr="chromeos">
         <message name="IDS_EXTERNAL_PROTOCOL_TITLE" desc="External Protocol Dialog Title">
-          Chromium OS cannot open this page.
+          Chromium OS can't open this page.
         </message>
       </if>
       <!-- Strings used to warn that an OS is not supported -->
       <if expr="is_win">
         <message name="IDS_UNSUPPORTED_OS_PRE_WIN_XP" desc="The text used to warn the user that Windows pre-XP is not supported">
           Chromium requires Windows XP or later. Some features may not work.
         </message>
       </if>
       <if expr="not chromeos">
         <message name="IDS_OPTIONS_RELAUNCH_REQUIRED" desc="The message displayed for an option that requires a relaunch to take effect. This appears in a message box if an option is changed that requires a relaunch.">
@@ skipping 954 matching lines @@
           Pin Chromium to your taskbar
         </message>
         <message name="IDS_WIN10_WELCOME_SELECT" desc="An instruction asking the user to select Chromium from an external list of apps.">
           Select <ph name="SMALL_PRODUCT_LOGO">&lt;div class="logo-small"&gt;&lt;/div&gt;</ph> <ph name="BEGIN_BOLD">&lt;strong&gt;</ph>Chromium<ph name="END_BOLD">&lt;/strong&gt;</ph>
         </message>
       </if>
 
     </messages>
   </release>
 </grit>