Enable pre-connect via {mouse,gesture}-event triggers to limited users controlled by Finch.

chrome/renderer/net/prescient_networking_dispatcher.cc

 // Copyright 2013 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 "chrome/renderer/net/prescient_networking_dispatcher.h"
 
+#include "base/metrics/field_trial.h"
 #include "chrome/common/render_messages.h"
 #include "content/public/renderer/render_thread.h"
 
 using WebKit::WebPrescientNetworking;
 
+const char kMouseEventPreconnectFieldTrialName[] = "MouseEventPreconnect";
+const char kMouseEventPreconnectFieldTrialMouseDownGroup[] = "MouseDown";
+const char kMouseEventPreconnectFieldTrialMouseOverGroup[] = "MouseOver";
+const char kMouseEventPreconnectFieldTrialTapUnconfirmedGroup[] =
+    "TapUnconfirmed";
+const char kMouseEventPreconnectFieldTrialTapDownGroup[] = "TapDown";
+
+namespace {
+
+// Returns true if preconnect is enabled for given motivation.
+// The preconnect via {mouse,gesture} event is enabled for limited userbase
+// for Finch field trial.
+bool isPreconnectEnabledForMotivation(
+    WebKit::WebPreconnectMotivation motivation) {
+  std::string group =
+      base::FieldTrialList::FindFullName(kMouseEventPreconnectFieldTrialName);
+
+  switch (motivation) {
+    case WebKit::WebPreconnectMotivationLinkMouseDown:
+      return group == kMouseEventPreconnectFieldTrialMouseDownGroup;
+    case WebKit::WebPreconnectMotivationLinkMouseOver:
+      return group == kMouseEventPreconnectFieldTrialMouseOverGroup;
+    case WebKit::WebPreconnectMotivationLinkTapUnconfirmed:
+      return group == kMouseEventPreconnectFieldTrialTapUnconfirmedGroup;
+    case WebKit::WebPreconnectMotivationLinkTapDown:
+      return group == kMouseEventPreconnectFieldTrialTapDownGroup;
+    default:
+      return false;
+  }
+}
+
+} // namespace
+
 PrescientNetworkingDispatcher::~PrescientNetworkingDispatcher() {
 }
 
 void PrescientNetworkingDispatcher::preconnect(
     const WebKit::WebURL& url,
     WebKit::WebPreconnectMotivation motivation) {
-  // FIXME(kouhei) actual pre-connecting is currently disabled.
-  // This should shortly be enabled via Finch field trials in upcoming patch.
-  // content::RenderThread::Get()->Send(new ChromeViewHostMsg_Preconnect(url));
+  if (!isPreconnectEnabledForMotivation(motivation)) {
+    return;
+  }
+
+  content::RenderThread::Get()->Send(new ChromeViewHostMsg_Preconnect(url));

[Nico, 2013/05/30 00:26:23]

If it fits in 80 cols, write

  if (isPrec…)
    RenderThread...->Send(…)

instead of the early return (unless you plan on adding more code down here)

[kouhei (in TOK), 2013/05/30 00:30:36]

Done.

 }