Added "Look Up in Dictionary" item to context menu for Mac.

chrome/app/generated_resources.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- This file contains definitions of resources that will be translated for
 each locale. -->
 
 <grit base_dir="." latest_public_release="0" current_release="1"
       source_lang_id="en" enc_check="möl">
   <outputs>
     <output filename="grit/generated_resources.h" type="rc_header">
       <emit emit_type='prepend'></emit>
@@ skipping 291 matching lines @@
           </message>
           <message name="IDS_CONTENT_CONTEXT_WRITING_DIRECTION_DEFAULT" desc="The name of the 'default' item from the Writing Direction submenu in the content area context menu.  To translate, launch /Applications/Textedit.app in an appropriately localized version of OS X, right-click on the text entry area and use the translation from there.">
             Default
           </message>
           <message name="IDS_CONTENT_CONTEXT_WRITING_DIRECTION_LTR" desc="The name of the 'Left to Right' item from the Writing Direction submenu in the content area context menu.  To translate, launch /Applications/Textedit.app in an appropriately localized version of OS X, right-click on the text entry area and use the translation from there.">
             Left to Right
           </message>
           <message name="IDS_CONTENT_CONTEXT_WRITING_DIRECTION_RTL" desc="The name of the 'Right to Left' item from the Writing Direction submenu in the content area context menu.  To translate, launch /Applications/Textedit.app in an appropriately localized version of OS X, right-click on the text entry area and use the translation from there.">
             Right to Left
           </message>
+          <message name="IDS_CONTENT_CONTEXT_LOOK_UP_IN_DICTIONARY" desc="The name of the 'Look Up in Dictionary' item in the content area context menu.  To translate, launch /Applications/Textedit.app in an appropriately localized version of OS X, right-click on the text entry area and use the translation from there.">
+            Look Up in Dictionary
+          </message>
       </if>
       <if expr="not pp_ifdef('use_titlecase')">
         <message name="IDS_CONTENT_CONTEXT_BACK" desc="The name of the Back command in the content area context menu">
           &amp;Back
         </message>
         <message name="IDS_CONTENT_CONTEXT_FORWARD" desc="The name of the Forward command in the content area context menu">
           &amp;Forward
         </message>
         <message name="IDS_CONTENT_CONTEXT_SAVEPAGEAS" desc="The name of the Save Page As command in the content area context menu">
           Save &amp;as...
@@ skipping 8832 matching lines @@
 
     </messages>
 
     <structures fallback_to_english="true">
       <structure name="IDD_CHROME_FRAME_FIND_DIALOG" file="cf_resources.rc" type="dialog" >
       </structure>
     </structures>
 
   </release>
 </grit>