Add option to open PDFs in system viewer to OS X and Linux.

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 0887e8bbea917a8f430ed2f826010831936887c6..6ea02c43c861b325c9822fc00c74cabb1846ee4c 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -2008,6 +2008,10 @@ Even if you have downloaded files from this website before, the website might ha
           desc="Download context menu: Open the download using the default handler for the platform.">
             Open with system viewer
           </message>
+          <message name="IDS_DOWNLOAD_MENU_PLATFORM_OPEN_ALWAYS"
+          desc="Download context menu: Always open the download using the default handler for the platform.">
+            Always open with system viewer
+          </message>
           <message name="IDS_DOWNLOAD_MENU_CANCEL"
                    desc="Download context menu: Cancel">
             &amp;Cancel
@@ -2068,6 +2072,10 @@ Even if you have downloaded files from this website before, the website might ha
                    desc="In Title Case: Download context menu: Open the download using the default handler for the platform.">
             Open With System Viewer
           </message>
+          <message name="IDS_DOWNLOAD_MENU_PLATFORM_OPEN_ALWAYS"
+                   desc="In Title Case: Download context menu: Always open the download using the default handler for the platform.">
+            Always Open With System Viewer
+          </message>
           <message name="IDS_DOWNLOAD_MENU_CANCEL"
                    desc="In Title Case: Download context menu: Cancel">
             &amp;Cancel
@@ -2099,7 +2107,7 @@ Even if you have downloaded files from this website before, the website might ha
         </if>  <!-- not use_titlecase -->
         <if expr="is_win">
           <message name="IDS_DOWNLOAD_MENU_ALWAYS_OPEN_PDF_IN_READER"
-                   desc="Download context menu: Open when download using Adobe Reader">
+                   desc="Download context menu: Always open PDFs using Adobe Reader">
             Always open in Adobe Reader
           </message>
         </if>