Fix punctuation of several Page Info strings

components/pageinfo_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <grit-part>
   <!-- Summary strings -->
   <message name="IDS_PAGEINFO_SECURE_SUMMARY" desc="A short summary phrase at the top of the Page Info bubble (which shows when you click the lock icon) that indicates that the connection to the current website is secure.">
     Secure connection
   </message>
   <message name="IDS_PAGEINFO_MIXED_CONTENT_SUMMARY" desc="A one-line summary at the top of the Page Info bubble (which shows when you click the security indicator) if the connection to the current website is using mainly using a secure connection but has some insecure parts (like insecurely loaded images).">
     Your connection to this site is not fully secure
   </message>
   <message name="IDS_PAGEINFO_NOT_SECURE_SUMMARY" desc="A one-line summary at the top of the Page Info bubble (which shows when you click the security indicator) if the connection to the current website is secure.">
@@ skipping 74 matching lines @@
   <message name="IDS_PAGE_INFO_SECURITY_TAB_UNABLE_TO_CHECK_REVOCATION" desc="The text of the identity section when we were unable to check if the certificate has been revoked.">
     Unable to check whether the certificate has been revoked.
   </message>
   <message name="IDS_PAGE_INFO_SECURITY_TAB_UNKNOWN_PARTY" desc="The default name used when we did not find a principal name.">
     unknown name
   </message>
   <message name="IDS_PAGE_INFO_SECURITY_TAB_WEAK_ENCRYPTION_CONNECTION_TEXT" desc="The text of the connection section when the connection uses weak encryption.">
     Your connection to <ph name="DOMAIN">$1<ex>www.google.com</ex></ph> is encrypted using an obsolete cipher suite.
   </message>
   <message name="IDS_PAGE_INFO_EXTENSION_PAGE" desc="Message to display in the page info bubble when the page you are on is a chrome-extension:// page. This refers to Chrome extensions.">
-    You are viewing an extension page.
+    You're viewing an extension page
   </message>
   <message name="IDS_PAGE_INFO_VIEW_SOURCE_PAGE" desc="Message to display in the page info bubble when you are viewing page sources by using |View page source| option from the right click menu.">
-    You are viewing the source of a web page.
+    You're viewing the source of a web page
   </message>
 
   <if expr="not use_titlecase">
     <message name="IDS_PAGEINFO_CERT_INFO_BUTTON" desc="Text of button in the page info that shows the SSL certificate.">
       Certificate information
     </message>
   </if>
   <if expr="use_titlecase">
     <message name="IDS_PAGEINFO_CERT_INFO_BUTTON" desc="In Title Case: Text of button in the page info that shows the SSL certificate.">
       Certificate Information
     </message>
   </if>
 </grit-part>