[mDns] Make DnsSdRegistry a leaky singleton

chrome/browser/extensions/api/mdns/mdns_api.h

 // Copyright 2013 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_API_MDNS_MDNS_API_H_
 #define CHROME_BROWSER_EXTENSIONS_API_MDNS_MDNS_API_H_
 
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
 #include "chrome/browser/media/router/discovery/mdns/dns_sd_registry.h"

[mark a. foltz, 2017/05/12 18:51:18]

Can this #include be moved to the .cc?  You have a forward declaration for
DnsSdRegistry below.

[zhaobin, 2017/05/12 21:15:59]

Remove forward declaration. This #include is needed for inheritance:

: public media_router::DnsSdRegistry::DnsSdObserver

 #include "chrome/common/extensions/api/mdns.h"
 #include "extensions/browser/api/async_api_function.h"
 #include "extensions/browser/browser_context_keyed_api_factory.h"
 #include "extensions/browser/event_router.h"
 #include "extensions/browser/extension_function.h"
 
 namespace content {
 class BrowserContext;
 }
 
@@ skipping 11 matching lines @@
                 public media_router::DnsSdRegistry::DnsSdObserver {
  public:
   explicit MDnsAPI(content::BrowserContext* context);
   ~MDnsAPI() override;
 
   static MDnsAPI* Get(content::BrowserContext* context);
 
   // BrowserContextKeyedAPI implementation.
   static BrowserContextKeyedAPIFactory<MDnsAPI>* GetFactoryInstance();
 
-  // Used to mock out the DnsSdRegistry for testing.
-  void SetDnsSdRegistryForTesting(
-      std::unique_ptr<media_router::DnsSdRegistry> registry);
+  // Used to mock out the DnsSdRegistry for testing. Does not take ownership of
+  // |registry|.
+  void SetDnsSdRegistryForTesting(media_router::DnsSdRegistry* registry);
 
   // Immediately issues a multicast DNS query for all service types.
   // NOTE: Discovery queries are sent to all event handlers associated with
   // |this| service's BrowserContext.
   void ForceDiscovery();
 
  protected:
   // Retrieve an instance of the registry. Lazily created when needed.
   virtual media_router::DnsSdRegistry* dns_sd_registry();
 
@@ skipping 44 matching lines @@
   // if non-null.
   // The counts for each service type are output to |service_type_counts|, if
   // non-null.
   void GetValidOnServiceListListeners(const std::string& service_type_filter,
                                       std::set<std::string>* extension_ids,
                                       ServiceTypeCounts* service_type_counts);
 
   // Ensure methods are only called on UI thread.
   base::ThreadChecker thread_checker_;
   content::BrowserContext* const browser_context_;
-  // Lazily created on first access and destroyed with this API class.
-  std::unique_ptr<media_router::DnsSdRegistry> dns_sd_registry_;
+  // Raw pointer to a leaky singleton. Lazily created on first access. Must
+  // outlive this object.
+  media_router::DnsSdRegistry* dns_sd_registry_;
   // Count of active listeners per service type, saved from the previous
   // invocation of UpdateMDnsListeners().
   ServiceTypeCounts prev_service_counts_;
 
   DISALLOW_COPY_AND_ASSIGN(MDnsAPI);
 };
 
 class MdnsForceDiscoveryFunction : public UIThreadExtensionFunction {
  public:
   MdnsForceDiscoveryFunction();
 
  protected:
   ~MdnsForceDiscoveryFunction() override;
 
  private:
   // UIThreadExtensionFunction override.
   ResponseAction Run() override;
 
   DECLARE_EXTENSION_FUNCTION("mdns.forceDiscovery", MDNS_FORCEDISCOVERY);
   DISALLOW_COPY_AND_ASSIGN(MdnsForceDiscoveryFunction);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_MDNS_MDNS_API_H_