Improve i18n descriptions based on clarifications requested.

chrome/app/settings_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Settings-specific strings (included from generated_resources.grd). -->
 <grit-part>
   <!-- About Page -->
   <if expr="chromeos">
     <message name="IDS_SETTINGS_ABOUT_PAGE_DETAILED_BUILD_INFO" desc="Label describing the section that shows detailed information about the current Chrome build.">
       Detailed build information
     </message>
     <message name="IDS_SETTINGS_ABOUT_PAGE_ARC_VERSION" desc="Label for ARC version">
       ARC Version
@@ skipping 331 matching lines @@
     Website
   </message>
   <message name="IDS_SETTINGS_PASSWORDS_USERNAME" desc="Label for the saved username when editing a password.">
     Username
   </message>
   <message name="IDS_SETTINGS_PASSWORDS_PASSWORD" desc="Label for the saved password when editing a password.">
     Password
   </message>
   <if expr="is_macosx">
     <then>
-      <message name="IDS_SETTINGS_PASSWORDS_MANAGE_PASSWORDS" desc="Shown in the passwords section of settings. Descriptive text to inform that passwords can be accessed online. Has a link. Also notifies mac users that chrome will sync passwords to the OS's Keychain, so their passwords will be synced to other chrome profiles.">
+      <message name="IDS_SETTINGS_PASSWORDS_MANAGE_PASSWORDS" desc="Shown in the passwords section of settings. Descriptive text to inform that passwords can be accessed online. Has a link. Also notifies mac users that chrome will sync passwords to the OS's Keychain, so their passwords will be synced to other chrome profiles. 'Keychain' is the name of a program on Mac and should not be translated.">
         Access your passwords from any device at <ph name="BEGIN_LINK">&lt;a is="action-link" href="$1" target="_blank"&gt;</ph>passwords.google.com<ph name="END_LINK">&lt;/a&gt;</ph>. On Mac, passwords may be saved to your Keychain and accessed or synced by other Chrome users sharing this OS X account.
       </message>
     </then>
     <else>
       <message name="IDS_SETTINGS_PASSWORDS_MANAGE_PASSWORDS" desc="Shown in the passwords section of settings. Descriptive text to inform that passwords can be accessed online. Has a link.">
         Access your passwords from any device at <ph name="BEGIN_LINK">&lt;a is="action-link" href="$1" target="_blank"&gt;</ph>passwords.google.com<ph name="END_LINK">&lt;/a&gt;</ph>
       </message>
     </else>
   </if>
 
@@ skipping 1430 matching lines @@
       System
     </message>
     <message name="IDS_SETTINGS_SYSTEM_HARDWARE_ACCELERATION_LABEL" desc="Label for the checkbox that forces Chrome to render via hardware acceleration (GPU) when available.">
       Use hardware acceleration when available
     </message>
     <message name="IDS_SETTINGS_SYSTEM_PROXY_SETTINGS_BUTTON" desc="Text for the button that changes a user's network proxy settings.">
       Change proxy settings
     </message>
   </if>
 </grit-part>