Revert CL 117933003. Re-add resource speculative prefetching code.

chrome/browser/predictors/resource_prefetch_predictor_tab_helper.cc

+// 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 "chrome/browser/predictors/resource_prefetch_predictor_tab_helper.h"
+
+#include "chrome/browser/predictors/resource_prefetch_predictor.h"
+#include "chrome/browser/predictors/resource_prefetch_predictor_factory.h"
+#include "chrome/browser/profiles/profile.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/load_from_memory_cache_details.h"
+
+DEFINE_WEB_CONTENTS_USER_DATA_KEY(
+    predictors::ResourcePrefetchPredictorTabHelper);
+
+using content::BrowserThread;
+
+namespace predictors {
+
+ResourcePrefetchPredictorTabHelper::ResourcePrefetchPredictorTabHelper(
+    content::WebContents* web_contents)
+    : content::WebContentsObserver(web_contents) {
+}
+
+ResourcePrefetchPredictorTabHelper::~ResourcePrefetchPredictorTabHelper() {
+}
+
+void ResourcePrefetchPredictorTabHelper::DocumentOnLoadCompletedInMainFrame() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  ResourcePrefetchPredictor* predictor =
+      ResourcePrefetchPredictorFactory::GetForProfile(
+          web_contents()->GetBrowserContext());
+  if (!predictor)
+    return;
+
+  NavigationID navigation_id(web_contents());
+  predictor->RecordMainFrameLoadComplete(navigation_id);
+}
+
+void ResourcePrefetchPredictorTabHelper::DidLoadResourceFromMemoryCache(
+    const content::LoadFromMemoryCacheDetails& details) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  ResourcePrefetchPredictor* predictor =
+      ResourcePrefetchPredictorFactory::GetForProfile(
+          web_contents()->GetBrowserContext());
+  if (!predictor)
+    return;
+
+  ResourcePrefetchPredictor::URLRequestSummary summary;
+  summary.navigation_id = NavigationID(web_contents());
+  summary.resource_url = details.url;
+  summary.mime_type = details.mime_type;
+  summary.resource_type =
+      ResourcePrefetchPredictor::GetResourceTypeFromMimeType(
+          details.mime_type, details.resource_type);
+  summary.was_cached = true;
+  predictor->RecordURLResponse(summary);
+}
+
+}  // namespace predictors