Introduce a separate preference for 'proxy server mode'

chrome/common/extensions/docs/samples.json

 {
   "api": {
     "chrome.bookmarks.create": "bookmarks.html#method-create", 
     "chrome.bookmarks.export": "bookmarks.html#method-export", 
     "chrome.bookmarks.get": "bookmarks.html#method-get", 
     "chrome.bookmarks.getChildren": "bookmarks.html#method-getChildren", 
     "chrome.bookmarks.getRecent": "bookmarks.html#method-getRecent", 
     "chrome.bookmarks.getTree": "bookmarks.html#method-getTree", 
     "chrome.bookmarks.import": "bookmarks.html#method-import", 
     "chrome.bookmarks.move": "bookmarks.html#method-move", 
@@ skipping 895 matching lines @@
       ], 
       "search_string": "IMAGEINFO GET IMAGE INFO FOR IMAGES, INCLUDING EXIF DATA BACKGROUND_PAGE CONTEXTMENUS TABS CHROME.CONTEXTMENUS.CREATE CHROME.TABS.GET CHROME.TABS.GETCURRENT CHROME.WINDOWS.CREATE CHROME.WINDOWS.UPDATE", 
       "source_files": [
         "background.html", 
         "imageinfo/binaryajax.js", 
         "imageinfo/exif.js", 
         "imageinfo/imageinfo.js", 
         "info.html", 
         "manifest.json"
       ], 
-      "source_hash": "672f49ed8edbe0829c7ba5a1d890b4440b157991", 
+      "source_hash": "c746d9114348f4b414c1ec05e988e2807feb963a", 
       "zip_path": "examples/extensions/imageinfo.zip"
     }, 
     {
       "api_calls": [
         "chrome.extension.getBackgroundPage", 
         "chrome.extension.onRequest", 
         "chrome.pageAction.hide", 
         "chrome.pageAction.setTitle", 
         "chrome.pageAction.show", 
         "chrome.tabs.get", 
@@ skipping 611 matching lines @@
       "source_files": [
         "manifest.json", 
         "typedUrls.html", 
         "typedUrls.js"
       ], 
       "source_hash": "72d5c3586feefc692c63039ce8bdb5f9d366c0e2", 
       "zip_path": "examples/api/history/showHistory.zip"
     }
   ]
 }