AppCache: Disable construction, copying and destruction in interfaces.

Interfaces are base classes that only consist of virtual methods. This
CL adds the following:
* deleted copy constructor and assignment - prevent unintended slicing
* protected constructors - prevent unintended direct instantiation
* protected destructors - prohibit the user of an interface
  implementation from destructing the implementation, enforcing that
  the user does not own the implementation

Change-Id: I2bb093e430cacb870846c74397051917ce50c83e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1663462
Commit-Queue: Victor Costan <pwnall@chromium.org>
Auto-Submit: Victor Costan <pwnall@chromium.org>
Reviewed-by: Staphany Park <staphany@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670255}

content/browser/appcache/appcache_group.h

@@ -47,9 +47,17 @@ class CONTENT_EXPORT AppCacheGroup
 
   class CONTENT_EXPORT UpdateObserver {
    public:
+    UpdateObserver(const UpdateObserver&) = delete;
+    UpdateObserver& operator=(const UpdateObserver&) = delete;
+
     // Called just after an appcache update has completed.
     virtual void OnUpdateComplete(AppCacheGroup* group) = 0;
-    virtual ~UpdateObserver() {}
+
+   protected:
+    // The constructor and destructor exist to facilitate subclassing, and
+    // should not be called directly.
+    UpdateObserver() noexcept = default;
+    virtual ~UpdateObserver() = default;
   };
 
   enum UpdateAppCacheStatus {

content/browser/appcache/appcache_host.h

@@ -61,13 +61,20 @@ class CONTENT_EXPORT AppCacheHost : public blink::mojom::AppCacheHost,
  public:
   class CONTENT_EXPORT Observer {
    public:
+    Observer(const Observer&) = delete;
+    Observer& operator=(const Observer&) = delete;
+
     // Called just after the cache selection algorithm completes.
     virtual void OnCacheSelectionComplete(AppCacheHost* host) = 0;
 
     // Called just prior to the instance being deleted.
     virtual void OnDestructionImminent(AppCacheHost* host) = 0;
 
-    virtual ~Observer() {}
+   protected:
+    // The constructor and destructor exist to facilitate subclassing, and
+    // should not be called directly.
+    Observer() noexcept = default;
+    virtual ~Observer() = default;
   };
 
   AppCacheHost(const base::UnguessableToken& host_id,

content/browser/appcache/appcache_service_impl.h

@@ -73,6 +73,9 @@ class CONTENT_EXPORT AppCacheServiceImpl : public AppCacheService {
 
   class CONTENT_EXPORT Observer {
    public:
+    Observer(const Observer&) = delete;
+    Observer& operator=(const Observer&) = delete;
+
     // Called just prior to the instance being deleted.
     virtual void OnServiceDestructionImminent(AppCacheServiceImpl* service) {}
 
@@ -82,7 +85,12 @@ class CONTENT_EXPORT AppCacheServiceImpl : public AppCacheService {
     // ref provided.
     virtual void OnServiceReinitialized(
         AppCacheStorageReference* old_storage_ref) {}
-    virtual ~Observer() {}
+
+   protected:
+    // The constructor and destructor exist to facilitate subclassing, and
+    // should not be called directly.
+    Observer() noexcept = default;
+    virtual ~Observer() = default;
   };
 
   // If not using quota management, the proxy may be NULL.

content/browser/appcache/appcache_storage.h

@@ -48,6 +48,9 @@ class CONTENT_EXPORT AppCacheStorage {
 
   class CONTENT_EXPORT Delegate {
    public:
+    Delegate(const Delegate&) = delete;
+    Delegate& operator=(const Delegate&) = delete;
+
     // If retrieval fails, 'collection' will be NULL.
     virtual void OnAllInfo(AppCacheInfoCollection* collection) {}
 
@@ -87,7 +90,10 @@ class CONTENT_EXPORT AppCacheStorage {
                                      const GURL& mainfest_url) {}
 
    protected:
-    virtual ~Delegate() {}
+    // The constructor and destructor exist to facilitate subclassing, and
+    // should not be called directly.
+    Delegate() noexcept = default;
+    virtual ~Delegate() = default;
   };
 
   explicit AppCacheStorage(AppCacheServiceImpl* service);