Adding `content_security_policy` to proxy sample extension.

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.getSubTree": "bookmarks.html#method-getSubTree",
     "chrome.bookmarks.getTree": "bookmarks.html#method-getTree",
     "chrome.bookmarks.import": "bookmarks.html#method-import",
@@ skipping 1855 matching lines @@
       "icon": "icon128.png",
       "id": "3e8e226d87e431296bb110b4f6eb7eec2ca7a826",
       "name": "Proxy Extension API Sample",
       "packaged_app": false,
       "path": "examples\/extensions\/proxy_configuration\/",
       "protocols": [],
       "search_string": "PROXY EXTENSION API SAMPLE SET CHROME-SPECIFIC PROXIES; A DEMONSTRATION OF CHROMES PROXY API BACKGROUND_PAGE BROWSER_ACTION POPUP PROXY CHROME.BROWSERACTION.SETBADGEBACKGROUNDCOLOR CHROME.BROWSERACTION.SETBADGETEXT CHROME.BROWSERACTION.SETTITLE CHROME.EXTENSION.ISALLOWEDINCOGNITOACCESS CHROME.EXTENSION.ONREQUEST CHROME.EXTENSION.SENDREQUEST CHROME.I18N.GETMESSAGE CHROME.PROXY.ONPROXYERROR",
       "source_files": [
         "_locales\/en\/messages.json",
         "background.html",
+        "background.js",
         "manifest.json",
+        "popup.css",
         "popup.html",
+        "popup.js",
         "proxy_error_handler.js",
         "proxy_form_controller.js",
         "test\/jsunittest.js",
         "test\/proxy_form_controller_test.html",
         "test\/proxy_form_controller_test.js",
         "test\/unittest.css"
       ],
-      "source_hash": "9378cbaff5c4aa3def4a92824b88146335feac44",
+      "source_hash": "10dfb898ef11aa9507bb07bcaa7cca5c51879f19",
       "zip_path": "examples\/extensions\/proxy_configuration.zip"
     },
     {
       "api_calls": [
         "chrome.browserAction.onClicked",
         "chrome.browserAction.setIcon",
         "chrome.extension.getBackgroundPage",
         "chrome.extension.getURL",
         "chrome.tabs.create",
         "chrome.tabs.get",
@@ skipping 433 matching lines @@
       "source_files": [
         "manifest.json",
         "popup.html",
         "sample.css"
       ],
       "source_hash": "c8bfc2b60f25c24dc3c5aaf75dd635c9419df66d",
       "zip_path": "examples\/api\/extension\/isAllowedAccess.zip"
     }
   ]
 }