[Media Router] Consistently refer to issue's learn more help page by ID.

chrome/browser/media/router/issue.cc

 // Copyright 2015 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.
 
 #include "base/guid.h"
 #include "chrome/browser/media/router/issue.h"
 
 namespace media_router {
 
 IssueAction::IssueAction(const IssueAction::Type type) : type_(type) {
 }
 
 IssueAction::~IssueAction() {
 }
 
 Issue::Issue(const std::string& title,
              const std::string& message,
              const IssueAction& default_action,
              const std::vector<IssueAction>& secondary_actions,
              const MediaRoute::Id& route_id,
              const Issue::Severity severity,
              bool is_blocking,
-             const std::string& help_url)
+             int help_page_id)
     : title_(title),
       message_(message),
       default_action_(default_action),
       secondary_actions_(secondary_actions),
       route_id_(route_id),
       severity_(severity),
       id_(base::GenerateGUID()),
       is_blocking_(is_blocking),
-      help_url_(GURL(help_url)) {
+      help_page_id_(help_page_id) {
   DCHECK(!title_.empty());
   DCHECK(severity_ != FATAL || is_blocking_) << "Severity is " << severity_;
 
   // Check that the default and secondary actions are not of the same type.
   if (!secondary_actions_.empty())
     DCHECK_NE(default_action_.type(), secondary_actions_[0].type());
 }
 
 Issue::Issue(const Issue& other) = default;
 
 Issue::~Issue() {
 }
 
 bool Issue::Equals(const Issue& other) const {
   return id_ == other.id_;
 }
 
 }  // namespace media_router