Adding ClearBlackList to the PreviewsBlackList and plumbing to UI

components/previews/core/previews_black_list.cc

Index: components/previews/core/previews_black_list.cc
diff --git a/components/previews/core/previews_black_list.cc b/components/previews/core/previews_black_list.cc
index f4b277b6f231ee0f0e6b4dca36c274bd30b29f94..fd1afed3b0ad23b33e14584d4e4fb0188546e89e 100644
--- a/components/previews/core/previews_black_list.cc
+++ b/components/previews/core/previews_black_list.cc
@@ -71,20 +71,53 @@ void PreviewsBlackList::AddPreviewNavigationSync(const GURL& url,
 bool PreviewsBlackList::IsLoadedAndAllowed(const GURL& url,
                                            PreviewsType type) const {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(url.has_host());
   if (!loaded_)
     return false;
   PreviewsBlackListItem* black_list_item = GetBlackListItem(url.host());
   return !black_list_item || !black_list_item->IsBlackListed(clock_->Now());
 }
 
+void PreviewsBlackList::ClearBlackList(base::Time begin_time,
+                                       base::Time end_time) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK_LE(begin_time, end_time);
+  // If the |black_list_item_map_| has been loaded from |opt_out_store_|,
+  // synchronous operations will be accurate. Otherwise, queue the task to run
+  // asynchronously.
+  if (loaded_) {
+    ClearBlackListSync(begin_time, end_time);
+  } else {
+    QueuePendingTask(base::Bind(&PreviewsBlackList::ClearBlackListSync,
+                                weak_factory_.GetWeakPtr(), begin_time,
+                                end_time));
+  }
+}
+
+void PreviewsBlackList::ClearBlackListSync(base::Time begin_time,
+                                           base::Time end_time) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(loaded_);
+  DCHECK_LE(begin_time, end_time);
+  black_list_item_map_.reset(nullptr);
+  loaded_ = false;
+  // Delete relevant entries and reload the blacklist into memory.
+  if (opt_out_store_) {
+    opt_out_store_->ClearBlackList(begin_time, end_time);

[tbansal1, 2016/10/04 00:16:59]

So, this means that opt out store must execute ClearBlackList  synchronously.
Right?

Alternatively, it might be more flexible if you make this async and let the opt
out store call LoadBlackListDone when it is done clearing the blacklist. 

[tbansal1, 2016/10/04 01:31:46]

Discard this comment.

+    opt_out_store_->LoadBlackList(base::Bind(
+        &PreviewsBlackList::LoadBlackListDone, weak_factory_.GetWeakPtr()));
+  } else {
+    LoadBlackListDone(base::MakeUnique<BlackListItemMap>());
+  }
+}
+
 void PreviewsBlackList::QueuePendingTask(base::Closure callback) {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(!loaded_);
   DCHECK(!callback.is_null());
   pending_callbacks_.emplace(callback);
 }
 
 void PreviewsBlackList::LoadBlackListDone(
     std::unique_ptr<BlackListItemMap> black_list_item_map) {
   DCHECK(thread_checker_.CalledOnValidThread());