Enable resource prefetch from the browser process.

chrome/renderer/prefetch_helper.cc

Index: chrome/renderer/prefetch_helper.cc
diff --git a/chrome/renderer/prefetch_helper.cc b/chrome/renderer/prefetch_helper.cc
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+// Copyright (c) 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 "chrome/renderer/prefetch_helper.h"
+
+#include "chrome/common/prefetch_messages.h"
+#include "content/public/renderer/render_frame.h"
+#include "third_party/WebKit/public/web/WebFrame.h"
+#include "third_party/WebKit/public/web/WebURLLoaderOptions.h"
+
+namespace prefetch {
+
+PrefetchHelper::PrefetchHelper(content::RenderFrame* render_frame)
+    : content::RenderFrameObserver(render_frame) {
+}
+
+PrefetchHelper::~PrefetchHelper() {
+  STLDeleteElements(&loader_set_);
+}
+
+bool PrefetchHelper::OnMessageReceived(
+    const IPC::Message& message) {
+  bool handled = true;
+  IPC_BEGIN_MESSAGE_MAP(PrefetchHelper, message)
+    IPC_MESSAGE_HANDLER(PrefetchMsg_Prefetch, OnPrefetch)
+    IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP()
+
+  return handled;
+}
+
+void PrefetchHelper::OnPrefetch(const GURL& url) {
+  blink::WebFrame* frame = render_frame()->GetWebFrame();
+  blink::WebURLRequest request(url);
+  request.setTargetType(blink::WebURLRequest::TargetIsPrefetch);
+  request.setPriority(blink::WebURLRequest::PriorityVeryLow);
+  blink::WebURLLoaderOptions options;
+  options.allowCredentials = true;
+  options.crossOriginRequestPolicy =
+      blink::WebURLLoaderOptions::CrossOriginRequestPolicyAllow;
+  blink::WebURLLoader* loader = frame->createAssociatedURLLoader(options);
+  loader->loadAsynchronously(request, this);
+  loader_set_.insert(loader);
+}
+
+void PrefetchHelper::didFinishLoading(blink::WebURLLoader* loader,
+                                      double finishTime,
+                                      int64_t totalEncodedDataLength) {
+  loader_set_.erase(loader);
+}
+
+void PrefetchHelper::didFail(blink::WebURLLoader* loader,
+                             const blink::WebURLError& error) {
+  loader_set_.erase(loader);
+}
+
+}  // namespace prefetch