Adds simple browser-side implementation for DNS prefetching.

components/dns_prefetch/browser/net_message_filter.cc

Index: components/dns_prefetch/browser/net_message_filter.cc
diff --git a/components/dns_prefetch/browser/net_message_filter.cc b/components/dns_prefetch/browser/net_message_filter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..268dc2ed314763d6eb3dd6221f5ee274b075acad
--- /dev/null
+++ b/components/dns_prefetch/browser/net_message_filter.cc
@@ -0,0 +1,93 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/dns_prefetch/browser/net_message_filter.h"
+
+#include "base/logging.h"
+#include "components/dns_prefetch/common/prefetch_common.h"
+#include "components/dns_prefetch/common/prefetch_messages.h"
+#include "ipc/ipc_message_macros.h"
+#include "net/base/address_list.h"
+#include "net/base/net_errors.h"
+#include "net/dns/host_resolver.h"
+#include "net/dns/single_request_host_resolver.h"
+#include "url/gurl.h"
+
+namespace dns_prefetch {
+
+namespace {
+
+const int kDefaultPort = 80;
+
+class DnsLookupRequest {
+ public:
+  DnsLookupRequest(net::HostResolver* host_resolver,
+                   const std::string& hostname)
+      : hostname_(hostname),
+        resolver_(host_resolver) {
+  }
+
+  // Return underlying network resolver status.
+  // net::OK ==> Host was found synchronously.
+  // net:ERR_IO_PENDING ==> Network will callback later with result.
+  // anything else ==> Host was not found synchronously.
+  int Start() {
+    net::HostResolver::RequestInfo resolve_info(
+        net::HostPortPair(hostname_, kDefaultPort));
+
+    // Make a note that this is a speculative resolve request. This allows
+    // separating it from real navigations in the observer's callback, and
+    // lets the HostResolver know it can be de-prioritized.
+    resolve_info.set_is_speculative(true);
+    return resolver_.Resolve(
+        resolve_info,
+        net::DEFAULT_PRIORITY,
+        &addresses_,
+        base::Bind(&DnsLookupRequest::OnLookupFinished, base::Owned(this)),
+        net::BoundNetLog());
+  }
+
+ private:
+  void OnLookupFinished(int result) {
+    VLOG(2) << __FUNCTION__ << ": " << hostname_ << ", result=" << result;
+  }
+
+  const std::string hostname_;
+  net::SingleRequestHostResolver resolver_;
+  net::AddressList addresses_;
+
+  DISALLOW_COPY_AND_ASSIGN(DnsLookupRequest);
+};
+
+}  // namespace
+
+NetMessageFilter::NetMessageFilter(net::HostResolver* host_resolver)
+    : content::BrowserMessageFilter(DnsPrefetchMsgStart),
+      host_resolver_(host_resolver) {
+  DCHECK(host_resolver_);
+}
+
+NetMessageFilter::~NetMessageFilter() {
+}
+
+bool NetMessageFilter::OnMessageReceived(const IPC::Message& message) {
+  bool handled = true;
+  IPC_BEGIN_MESSAGE_MAP(NetMessageFilter, message)
+    IPC_MESSAGE_HANDLER(DnsPrefetchMsg_RequestPrefetch, OnDnsPrefetch)
+    IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP()
+  return handled;
+}
+
+void NetMessageFilter::OnDnsPrefetch(const LookupRequest& lookup_request) {
+  DCHECK(host_resolver_);
+  for (const std::string& hostname : lookup_request.hostname_list) {
+    DnsLookupRequest* request = new DnsLookupRequest(host_resolver_, hostname);
+    // Note: DnsLookupRequest will be freed by the base::Owned call when
+    // resolving has completed.
+    request->Start();
+  }
+}
+
+}  // namespace dns_prefetch