Adding a short blacklist period after every previews opt out

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 896507deee1e3391ed33a620df2b9e2777e7eba6..ee4877040b1d81a76b2bbf241346a53c188eee48 100644
--- a/components/previews/core/previews_black_list.cc
+++ b/components/previews/core/previews_black_list.cc
@@ -55,20 +55,23 @@ PreviewsBlackList::PreviewsBlackList(
   }
 }
 
 PreviewsBlackList::~PreviewsBlackList() {}
 
 void PreviewsBlackList::AddPreviewNavigation(const GURL& url,
                                              bool opt_out,
                                              PreviewsType type) {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(url.has_host());
+  if (opt_out) {
+    last_opt_out_time_ = clock_->Now();
+  }
   // 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_) {
     AddPreviewNavigationSync(url, opt_out, type);
   } else {
     QueuePendingTask(base::Bind(&PreviewsBlackList::AddPreviewNavigationSync,
                                 base::Unretained(this), url, opt_out, type));
   }
 }
@@ -90,20 +93,25 @@ void PreviewsBlackList::AddPreviewNavigationSync(const GURL& url,
     return;
   opt_out_store_->AddPreviewNavigation(opt_out, host_name, type, now);
 }
 
 bool PreviewsBlackList::IsLoadedAndAllowed(const GURL& url,

[tbansal1, 2016/10/25 00:47:41]

At some point in future, it might be useful for this function to return an enum
describing why the preview can;t be shown. Consumers can than use it to record
UMA (which can help them in understanding how to tune different field trial
params).

[RyanSturm, 2016/10/25 17:15:38]

Agreed. Seperate CL when someone wants it. We'd need to "correctly" order them
here and in the method that calls this.

                                            PreviewsType type) const {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(url.has_host());
   if (!loaded_)
     return false;
+  if (last_opt_out_time_ &&
+      clock_->Now() <
+          last_opt_out_time_.value() + params::SingleOptOutDuration()) {
+    return false;
+  }
   PreviewsBlackListItem* black_list_item =
       GetBlackListItem(*black_list_item_map_, 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_|,