Remove methods that modify cookie storage at runtime (see issue #2622).

This change removes cookie and request handler functionality that will not
supported by the NetworkService. Specifically, it is no longer possible to
change cookie storage locations at runime by returning a different
CefCookieManager for an already initialized CefRequestContext. After this change
you will need to use a separate CefRequestContext when creating a CefBrowser if
you require separate cookie storage.

The following methods have been removed:
- CefCookieManager::CreateManager
- CefCookieManager::GetBlockingManager
- CefCookieManager::SetStoragePath
- CefRequestContextHandler::GetCookieManager

The following methods have been renamed:
- CefRequestContext::GetDefaultCookieManager to GetCookieManager.

This change substantially simplifies the network implementation in CEF because
it is no longer necessary to proxy objects that are normally owned by Chromium.
Chromium patches that are no longer necessary will be removed as a follow-up
commit.

To test: Verify that `ceftests --gtest_filter=-PluginTest.*` pass with
NetworkService disabled. Plugin tests will be fixed in a follow-up commit.

include/cef_request_context_handler.h

@@ -39,7 +39,6 @@
 #pragma once
 
 #include "include/cef_base.h"
-#include "include/cef_cookie.h"
 #include "include/cef_web_plugin.h"
 
 class CefRequestContext;
@@ -62,14 +61,6 @@ class CefRequestContextHandler : public virtual CefBaseRefCounted {
   virtual void OnRequestContextInitialized(
       CefRefPtr<CefRequestContext> request_context) {}
 
-  ///
-  // Called on the browser process IO thread to retrieve the cookie manager. If
-  // this method returns NULL the default cookie manager retrievable via
-  // CefRequestContext::GetDefaultCookieManager() will be used.
-  ///
-  /*--cef()--*/
-  virtual CefRefPtr<CefCookieManager> GetCookieManager() { return NULL; }
-
   ///
   // Called on multiple browser process threads before a plugin instance is
   // loaded. |mime_type| is the mime type of the plugin that will be loaded.