Simplify HostZoomLevelContext lifetime

The HostZoomLevelContext class was refcounted, but only ever owned by
a StoragePartitionImpl so remove the refcounting. It also had a custom
deleter doing basically the same work as DeleteOnUIThread so use that
instead. De-virtualize the destructor, too.

Change-Id: I75bf780953e6420e00d488af1560262ca4ed7188
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2028934
Auto-Submit: Joshua Bell <jsbell@chromium.org>
Commit-Queue: James MacLean <wjmaclean@chromium.org>
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743119}

content/browser/host_zoom_level_context.cc

@@ -6,11 +6,7 @@
 
 #include <utility>
 
-#include "base/files/file_path.h"
-#include "base/task/post_task.h"
 #include "content/browser/host_zoom_map_impl.h"
-#include "content/public/browser/browser_task_traits.h"
-#include "content/public/browser/browser_thread.h"
 
 namespace content {
 
@@ -22,15 +18,6 @@ HostZoomLevelContext::HostZoomLevelContext(
     zoom_level_delegate_->InitHostZoomMap(host_zoom_map_impl_.get());
 }
 
-HostZoomLevelContext::~HostZoomLevelContext() {}
-
-void HostZoomLevelContext::DeleteOnCorrectThread() const {
-  if (BrowserThread::IsThreadInitialized(BrowserThread::UI) &&
-      !BrowserThread::CurrentlyOn(BrowserThread::UI)) {
-    base::DeleteSoon(FROM_HERE, {BrowserThread::UI}, this);
-    return;
-  }
-  delete this;
-}
+HostZoomLevelContext::~HostZoomLevelContext() = default;
 
 }  // namespace content

content/browser/host_zoom_level_context.h

@@ -8,19 +8,17 @@
 #include <memory>
 
 #include "base/macros.h"
-#include "base/memory/ref_counted.h"
 #include "content/browser/host_zoom_map_impl.h"
+#include "content/public/browser/browser_thread.h"
 #include "content/public/browser/zoom_level_delegate.h"
 
 namespace content {
-struct HostZoomLevelContextDeleter;
 
 // This class manages a HostZoomMap and associates it with a ZoomLevelDelegate,
 // if one is provided. It also serves to keep the zoom level machinery details
-// separate from the owning StoragePartitionImpl.
-class HostZoomLevelContext
-    : public base::RefCountedThreadSafe<HostZoomLevelContext,
-                                        HostZoomLevelContextDeleter> {
+// separate from the owning StoragePartitionImpl. It must be destroyed on the
+// UI thread.
+class HostZoomLevelContext {
  public:
   explicit HostZoomLevelContext(
       std::unique_ptr<ZoomLevelDelegate> zoom_level_delegate);
@@ -30,16 +28,11 @@ class HostZoomLevelContext
     return zoom_level_delegate_.get();
   }
 
- protected:
-  virtual ~HostZoomLevelContext();
-
  private:
+  friend struct BrowserThread::DeleteOnThread<BrowserThread::UI>;
   friend class base::DeleteHelper<HostZoomLevelContext>;
-  friend class base::RefCountedThreadSafe<HostZoomLevelContext,
-                                          HostZoomLevelContextDeleter>;
-  friend struct HostZoomLevelContextDeleter;
 
-  void DeleteOnCorrectThread() const;
+  ~HostZoomLevelContext();
 
   std::unique_ptr<HostZoomMapImpl> host_zoom_map_impl_;
   // Release the delegate before the HostZoomMap, in case it is carrying
@@ -49,12 +42,6 @@ class HostZoomLevelContext
   DISALLOW_COPY_AND_ASSIGN(HostZoomLevelContext);
 };
 
-struct HostZoomLevelContextDeleter {
-  static void Destruct(const HostZoomLevelContext* context) {
-    context->DeleteOnCorrectThread();
-  }
-};
-
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_HOST_ZOOM_LEVEL_CONTEXT_H_

content/browser/storage_partition_impl.cc

@@ -1419,8 +1419,8 @@ void StoragePartitionImpl::Initialize() {
       browser_context_, service_worker_context_);
 
 #if !defined(OS_ANDROID)
-  host_zoom_level_context_ = new HostZoomLevelContext(
-      browser_context_->CreateZoomLevelDelegate(partition_path_));
+  host_zoom_level_context_.reset(new HostZoomLevelContext(
+      browser_context_->CreateZoomLevelDelegate(partition_path_)));
 #endif  // !defined(OS_ANDROID)
 
   platform_notification_context_ = new PlatformNotificationContextImpl(

content/browser/storage_partition_impl.h

@@ -476,7 +476,8 @@ class CONTENT_EXPORT StoragePartitionImpl
   std::unique_ptr<PushMessagingContext> push_messaging_context_;
   scoped_refptr<storage::SpecialStoragePolicy> special_storage_policy_;
 #if !defined(OS_ANDROID)
-  scoped_refptr<HostZoomLevelContext> host_zoom_level_context_;
+  std::unique_ptr<HostZoomLevelContext, BrowserThread::DeleteOnUIThread>
+      host_zoom_level_context_;
 #endif  // !defined(OS_ANDROID)
   scoped_refptr<PlatformNotificationContextImpl> platform_notification_context_;
   scoped_refptr<BackgroundFetchContext> background_fetch_context_;