<webview>: Remove broken captureVisibleRegion code until feature is properly supported

extensions/renderer/resources/guest_view/web_view_experimental.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This module implements experimental API for <webview>.
 // See web_view.js for details.
 //
 // <webview> Experimental API is only available on canary and dev channels of
 // Chrome.
 
 var WebView = require('webView').WebView;
 var WebViewInternal = require('webViewInternal').WebViewInternal;
 
 // Returns a map of experimental <webview> DOM event names to their associated
 // extension event descriptor objects. See |WEB_VIEW_EVENTS| in
 // web_view_events.js for more information and details on how this map should
 // be formatted.
 WebView.prototype.maybeGetExperimentalEvents = function() {
   return {};
 };
 
-// Captures the visible content within the webview.
-WebView.prototype.captureVisibleRegion = function(spec, callback) {
-  WebViewInternal.captureVisibleRegion(this.guestInstanceId, spec, callback);
-};
-
 // Loads a data URL with a specified base URL used for relative links.
 // Optionally, a virtual URL can be provided to be shown to the user instead
 // of the data URL.
 WebView.prototype.loadDataWithBaseUrl = function(
     dataUrl, baseUrl, virtualUrl) {
   if (!this.guestInstanceId) {
     return;
   }
   WebViewInternal.loadDataWithBaseUrl(
       this.guestInstanceId, dataUrl, baseUrl, virtualUrl, function() {
         // Report any errors.
         if (chrome.runtime.lastError != undefined) {
           window.console.error(
               'Error while running webview.loadDataWithBaseUrl: ' +
                   chrome.runtime.lastError.message);
         }
       });
 };
 
 // Registers the experimantal WebVIew API when available.
 WebView.maybeGetExperimentalAPIs = function() {
   var experimentalMethods = [
-    'captureVisibleRegion',
     'loadDataWithBaseUrl'
   ];
   return experimentalMethods;
 };