Implement host-based deletion for the hostname resolution cache.

net/dns/host_cache.cc

Index: net/dns/host_cache.cc
diff --git a/net/dns/host_cache.cc b/net/dns/host_cache.cc
index 7556e7eee478408afd182eef19360fafc3681ffe..ee50f8626131883117e534312428f64d3422d99e 100644
--- a/net/dns/host_cache.cc
+++ b/net/dns/host_cache.cc
@@ -198,6 +198,27 @@ void HostCache::clear() {
   entries_.clear();
 }
 
+void HostCache::ClearForHosts(
+    const base::Callback<bool(const std::string&)>& host_filter) {
+  DCHECK(CalledOnValidThread());
+
+  if (host_filter.is_null()) {
+    clear();
+    return;
+  }
+
+  for (EntryMap::iterator it = entries_.begin(); it != entries_.end();) {
+    EntryMap::iterator next_it = std::next(it);
+
+    if (host_filter.Run(it->first.hostname)) {
+      RecordErase(ERASE_CLEAR, base::TimeTicks::Now(), it->second);

[mmenke, 2016/08/31 15:24:37]

Maybe just call base::TimeTicks::Now() once, outside of the loop?  Not sure how
expensive it is, and this is called rarely enough that it probably doesn't
really matter, but does seem like we don't need to keep on getting the time.

[msramek, 2016/08/31 16:02:55]

Done. Good point - it's even better for consistency, as clear() also uses the
same timestamp for all entries.

+      entries_.erase(it);
+    }
+
+    it = next_it;
+  }
+}
+
 size_t HostCache::size() const {
   DCHECK(CalledOnValidThread());
   return entries_.size();