Allowing Search Prefetch responses to be served from cache on BF

BF and restore navigations are allowed to use cache even when the
cache-control headers would otherwise require revalidation. When this
occurs on a previously served Search Prefetch URL, Chrome should attempt
to serve the prefetch response from cache, and then fallback to the
navigation URL on the network.

Bug: 1162121
Change-Id: I5ec8c82fe772e57acce812987efed2baa3301ed2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2605414Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840219}

chrome/browser/BUILD.gn

@@ -1365,6 +1365,8 @@ static_library("browser") {
     "prefetch/prefetch_proxy/prefetch_proxy_url_loader_interceptor.h",
     "prefetch/prefetch_proxy/prefetched_mainframe_response_container.cc",
     "prefetch/prefetch_proxy/prefetched_mainframe_response_container.h",
+    "prefetch/search_prefetch/back_forward_search_prefetch_url_loader.cc",
+    "prefetch/search_prefetch/back_forward_search_prefetch_url_loader.h",
     "prefetch/search_prefetch/base_search_prefetch_request.cc",
     "prefetch/search_prefetch/base_search_prefetch_request.h",
     "prefetch/search_prefetch/field_trial_settings.cc",

chrome/browser/prefetch/search_prefetch/back_forward_search_prefetch_url_loader.cc

+// Copyright 2020 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/prefetch/search_prefetch/back_forward_search_prefetch_url_loader.h"
+
+#include <string>
+#include <utility>
+
+#include "base/bind.h"
+#include "base/location.h"
+#include "base/memory/ptr_util.h"
+#include "base/task/post_task.h"
+#include "base/task/task_traits.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "base/time/time.h"
+#include "chrome/browser/prefetch/search_prefetch/search_prefetch_service.h"
+#include "chrome/browser/prefetch/search_prefetch/search_prefetch_service_factory.h"
+#include "chrome/browser/profiles/profile.h"
+#include "content/public/browser/storage_partition.h"
+#include "net/base/load_flags.h"
+#include "net/http/http_response_headers.h"
+#include "net/http/http_status_code.h"
+#include "net/http/http_util.h"
+#include "net/traffic_annotation/network_traffic_annotation.h"
+#include "services/network/public/cpp/constants.h"
+#include "services/network/public/cpp/resource_request.h"
+#include "services/network/public/cpp/shared_url_loader_factory.h"
+#include "url/gurl.h"
+
+BackForwardSearchPrefetchURLLoader::BackForwardSearchPrefetchURLLoader(
+    Profile* profile,
+    const net::NetworkTrafficAnnotationTag& network_traffic_annotation,
+    const GURL& prefetch_url)
+    : profile_(profile),
+      network_traffic_annotation_(network_traffic_annotation),
+      prefetch_url_(prefetch_url) {}
+
+BackForwardSearchPrefetchURLLoader::~BackForwardSearchPrefetchURLLoader() =
+    default;
+
+SearchPrefetchURLLoader::RequestHandler
+BackForwardSearchPrefetchURLLoader::ServingResponseHandler(
+    std::unique_ptr<SearchPrefetchURLLoader> loader) {
+  return base::BindOnce(
+      &BackForwardSearchPrefetchURLLoader::SetUpForwardingClient,
+      weak_factory_.GetWeakPtr(), std::move(loader));
+}
+
+void BackForwardSearchPrefetchURLLoader::SetUpForwardingClient(
+    std::unique_ptr<SearchPrefetchURLLoader> loader,
+    const network::ResourceRequest& resource_request,
+    mojo::PendingReceiver<network::mojom::URLLoader> receiver,
+    mojo::PendingRemote<network::mojom::URLLoaderClient> forwarding_client) {
+  resource_request_ =
+      std::make_unique<network::ResourceRequest>(resource_request);
+
+  network::ResourceRequest prefetch_request = *resource_request_;
+
+  prefetch_request.load_flags |= net::LOAD_ONLY_FROM_CACHE;
+  prefetch_request.url = prefetch_url_;
+
+  auto url_loader_factory =
+      content::BrowserContext::GetDefaultStoragePartition(profile_)
+          ->GetURLLoaderFactoryForBrowserProcess();
+
+  // Create a network service URL loader with passed in params.
+  url_loader_factory->CreateLoaderAndStart(
+      network_url_loader_.BindNewPipeAndPassReceiver(), 0, 0,
+      network::mojom::kURLLoadOptionNone, prefetch_request,
+      url_loader_receiver_.BindNewPipeAndPassRemote(
+          base::ThreadTaskRunnerHandle::Get()),
+      net::MutableNetworkTrafficAnnotationTag(network_traffic_annotation_));
+  url_loader_receiver_.set_disconnect_handler(base::BindOnce(
+      &BackForwardSearchPrefetchURLLoader::MojoDisconnectForPrefetch,
+      base::Unretained(this)));
+
+  // Bind to the content/ navigation code.
+  DCHECK(!receiver_.is_bound());
+
+  // At this point, we are bound to the mojo receiver, so we can release
+  // |loader|, which points to |this|.
+  receiver_.Bind(std::move(receiver));
+  loader.release();
+  receiver_.set_disconnect_handler(base::BindOnce(
+      &BackForwardSearchPrefetchURLLoader::MojoDisconnectWithNoFallback,
+      weak_factory_.GetWeakPtr()));
+  forwarding_client_.Bind(std::move(forwarding_client));
+}
+
+void BackForwardSearchPrefetchURLLoader::RestartDirect() {
+  network_url_loader_.reset();
+  url_loader_receiver_.reset();
+  can_fallback_ = false;
+
+  SearchPrefetchService* service =
+      SearchPrefetchServiceFactory::GetForProfile(profile_);
+  if (service)
+    service->ClearCacheEntry(resource_request_->url);
+
+  auto url_loader_factory =
+      content::BrowserContext::GetDefaultStoragePartition(profile_)
+          ->GetURLLoaderFactoryForBrowserProcess();
+
+  // Create a network service URL loader with passed in params.
+  url_loader_factory->CreateLoaderAndStart(
+      network_url_loader_.BindNewPipeAndPassReceiver(), 0, 0,
+      network::mojom::kURLLoadOptionNone, *resource_request_,
+      url_loader_receiver_.BindNewPipeAndPassRemote(
+          base::ThreadTaskRunnerHandle::Get()),
+      net::MutableNetworkTrafficAnnotationTag(network_traffic_annotation_));
+  url_loader_receiver_.set_disconnect_handler(base::BindOnce(
+      &BackForwardSearchPrefetchURLLoader::MojoDisconnectWithNoFallback,
+      base::Unretained(this)));
+  if (paused_) {
+    network_url_loader_->PauseReadingBodyFromNet();
+  }
+}
+
+void BackForwardSearchPrefetchURLLoader::OnReceiveResponse(
+    network::mojom::URLResponseHeadPtr head) {
+  DCHECK(forwarding_client_);
+  if (can_fallback_) {
+    if (!head->headers) {
+      RestartDirect();
+      return;
+    }
+
+    // Any 200 response can be served.
+    if (head->headers->response_code() < net::HTTP_OK ||
+        head->headers->response_code() >= net::HTTP_MULTIPLE_CHOICES) {
+      RestartDirect();
+      return;
+    }
+    url_loader_receiver_.set_disconnect_handler(base::BindOnce(
+        &BackForwardSearchPrefetchURLLoader::MojoDisconnectWithNoFallback,
+        weak_factory_.GetWeakPtr()));
+
+    SearchPrefetchService* service =
+        SearchPrefetchServiceFactory::GetForProfile(profile_);
+    if (service)
+      service->UpdateServeTime(resource_request_->url);
+  }
+
+  can_fallback_ = false;
+  forwarding_client_->OnReceiveResponse(std::move(head));
+}
+
+void BackForwardSearchPrefetchURLLoader::OnReceiveRedirect(
+    const net::RedirectInfo& redirect_info,
+    network::mojom::URLResponseHeadPtr head) {
+  DCHECK(forwarding_client_);
+  if (can_fallback_) {
+    RestartDirect();
+    return;
+  }
+
+  forwarding_client_->OnReceiveRedirect(redirect_info, std::move(head));
+}
+
+void BackForwardSearchPrefetchURLLoader::OnUploadProgress(
+    int64_t current_position,
+    int64_t total_size,
+    OnUploadProgressCallback callback) {
+  // We only handle GETs.
+  NOTREACHED();
+}
+
+void BackForwardSearchPrefetchURLLoader::OnReceiveCachedMetadata(
+    mojo_base::BigBuffer data) {
+  // Do nothing. This is not supported for navigation loader.
+}
+
+void BackForwardSearchPrefetchURLLoader::OnTransferSizeUpdated(
+    int32_t transfer_size_diff) {
+  DCHECK(forwarding_client_);
+  forwarding_client_->OnTransferSizeUpdated(transfer_size_diff);
+}
+
+void BackForwardSearchPrefetchURLLoader::OnStartLoadingResponseBody(
+    mojo::ScopedDataPipeConsumerHandle body) {
+  DCHECK(forwarding_client_);
+  forwarding_client_->OnStartLoadingResponseBody(std::move(body));
+  return;
+}
+
+void BackForwardSearchPrefetchURLLoader::OnComplete(
+    const network::URLLoaderCompletionStatus& status) {
+  if (status.error_code != net::OK && can_fallback_) {
+    RestartDirect();
+    return;
+  }
+  DCHECK(forwarding_client_);
+  can_fallback_ = false;
+  forwarding_client_->OnComplete(status);
+  network_url_loader_.reset();
+}
+
+void BackForwardSearchPrefetchURLLoader::FollowRedirect(
+    const std::vector<std::string>& removed_headers,
+    const net::HttpRequestHeaders& modified_headers,
+    const net::HttpRequestHeaders& modified_cors_exempt_headers,
+    const base::Optional<GURL>& new_url) {
+  // This should never be called for a non-network service URLLoader.
+  NOTREACHED();
+}
+
+void BackForwardSearchPrefetchURLLoader::SetPriority(
+    net::RequestPriority priority,
+    int32_t intra_priority_value) {
+  // Pass through.
+  if (network_url_loader_)
+    network_url_loader_->SetPriority(priority, intra_priority_value);
+
+  resource_request_->priority = priority;
+}
+
+void BackForwardSearchPrefetchURLLoader::PauseReadingBodyFromNet() {
+  // Pass through.
+  if (network_url_loader_)
+    network_url_loader_->PauseReadingBodyFromNet();
+  paused_ = true;
+}
+
+void BackForwardSearchPrefetchURLLoader::ResumeReadingBodyFromNet() {
+  // Pass through.
+  if (network_url_loader_)
+    network_url_loader_->ResumeReadingBodyFromNet();
+  paused_ = false;
+}
+
+void BackForwardSearchPrefetchURLLoader::MojoDisconnectForPrefetch() {
+  if (can_fallback_)
+    RestartDirect();
+}
+
+void BackForwardSearchPrefetchURLLoader::MojoDisconnectWithNoFallback() {
+  delete this;
+}

chrome/browser/prefetch/search_prefetch/back_forward_search_prefetch_url_loader.h

+// Copyright 2020 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.
+
+#ifndef CHROME_BROWSER_PREFETCH_SEARCH_PREFETCH_BACK_FORWARD_SEARCH_PREFETCH_URL_LOADER_H_
+#define CHROME_BROWSER_PREFETCH_SEARCH_PREFETCH_BACK_FORWARD_SEARCH_PREFETCH_URL_LOADER_H_
+
+#include <vector>
+
+#include "base/callback.h"
+#include "base/memory/scoped_refptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/optional.h"
+#include "chrome/browser/prefetch/search_prefetch/search_prefetch_url_loader.h"
+#include "chrome/browser/prefetch/search_prefetch/streaming_search_prefetch_request.h"
+#include "content/public/browser/url_loader_request_interceptor.h"
+#include "mojo/public/cpp/bindings/pending_receiver.h"
+#include "mojo/public/cpp/bindings/pending_remote.h"
+#include "mojo/public/cpp/bindings/receiver.h"
+#include "mojo/public/cpp/bindings/remote.h"
+#include "services/network/public/mojom/url_loader.mojom-forward.h"
+#include "services/network/public/mojom/url_response_head.mojom-forward.h"
+
+// This class tries to fetch a prefetch response from cache, and if one is not
+// available, it fetches the non-prefetch URL directly. This case is only
+// triggered when cache doesn't need to be revalidated (i.e., back/forward).
+class BackForwardSearchPrefetchURLLoader
+    : public network::mojom::URLLoader,
+      public network::mojom::URLLoaderClient,
+      public SearchPrefetchURLLoader {
+ public:
+  // Creates and stores state needed to do the cache lookup.
+  BackForwardSearchPrefetchURLLoader(
+      Profile* profile,
+      const net::NetworkTrafficAnnotationTag& network_traffic_annotation,
+      const GURL& prefetch_url);
+
+  ~BackForwardSearchPrefetchURLLoader() override;
+
+ private:
+  // SearchPrefetchURLLoader:
+  SearchPrefetchURLLoader::RequestHandler ServingResponseHandler(
+      std::unique_ptr<SearchPrefetchURLLoader> loader) override;
+
+  // network::mojom::URLLoader:
+  void FollowRedirect(
+      const std::vector<std::string>& removed_headers,
+      const net::HttpRequestHeaders& modified_headers,
+      const net::HttpRequestHeaders& modified_cors_exempt_headers,
+      const base::Optional<GURL>& new_url) override;
+  void SetPriority(net::RequestPriority priority,
+                   int32_t intra_priority_value) override;
+  void PauseReadingBodyFromNet() override;
+  void ResumeReadingBodyFromNet() override;
+
+  // network::mojom::URLLoaderClient
+  void OnReceiveResponse(network::mojom::URLResponseHeadPtr head) override;
+  void OnReceiveRedirect(const net::RedirectInfo& redirect_info,
+                         network::mojom::URLResponseHeadPtr head) override;
+  void OnUploadProgress(int64_t current_position,
+                        int64_t total_size,
+                        OnUploadProgressCallback callback) override;
+  void OnReceiveCachedMetadata(mojo_base::BigBuffer data) override;
+  void OnTransferSizeUpdated(int32_t transfer_size_diff) override;
+  void OnStartLoadingResponseBody(
+      mojo::ScopedDataPipeConsumerHandle body) override;
+  void OnComplete(const network::URLLoaderCompletionStatus& status) override;
+
+  // Restarts the request to go directly to |resource_request_|.
+  void RestartDirect();
+
+  // The disconnect handler that is used for the fetch of the cached prefetch
+  // response. This handler is not used once a fallback is started or serving is
+  // started.
+  void MojoDisconnectForPrefetch();
+
+  // This handler is used for forwarding client errors and errors after a
+  // fallback can not occur.
+  void MojoDisconnectWithNoFallback();
+
+  // Sets up mojo forwarding to the navigation path. Resumes
+  // |network_url_loader_| calls. Serves the start of the response to the
+  // navigation path. After this method is called, |this| manages its own
+  // lifetime; |loader| points to |this| and can be released once the mojo
+  // connection is set up.
+  void SetUpForwardingClient(
+      std::unique_ptr<SearchPrefetchURLLoader> loader,
+      const network::ResourceRequest&,
+      mojo::PendingReceiver<network::mojom::URLLoader> receiver,
+      mojo::PendingRemote<network::mojom::URLLoaderClient> forwarding_client);
+
+  // The network URLLoader that fetches the prefetch URL and its receiver.
+  mojo::Remote<network::mojom::URLLoader> network_url_loader_;
+  mojo::Receiver<network::mojom::URLLoaderClient> url_loader_receiver_{this};
+
+  // The request that is being prefetched.
+  std::unique_ptr<network::ResourceRequest> resource_request_;
+
+  // Whether we are serving from |bdoy_content_|.
+  bool can_fallback_ = true;
+
+  // If the owner paused network activity, we need to propagate that if a
+  // fallback occurs.
+  bool paused_ = false;
+
+  Profile* profile_;
+
+  net::NetworkTrafficAnnotationTag network_traffic_annotation_;
+
+  // The URL for the prefetch response stored in cache.
+  GURL prefetch_url_;
+
+  // Forwarding client receiver.
+  mojo::Receiver<network::mojom::URLLoader> receiver_{this};
+  mojo::Remote<network::mojom::URLLoaderClient> forwarding_client_;
+
+  base::WeakPtrFactory<BackForwardSearchPrefetchURLLoader> weak_factory_{this};
+};
+
+#endif  // CHROME_BROWSER_PREFETCH_SEARCH_PREFETCH_BACK_FORWARD_SEARCH_PREFETCH_URL_LOADER_H_

chrome/browser/prefetch/search_prefetch/base_search_prefetch_request.cc

@@ -94,9 +94,10 @@ BaseSearchPrefetchRequest::BaseSearchPrefetchRequest(
 
 BaseSearchPrefetchRequest::~BaseSearchPrefetchRequest() = default;
 
-bool BaseSearchPrefetchRequest::StartPrefetchRequest(Profile* profile) {
-  net::NetworkTrafficAnnotationTag network_traffic_annotation =
-      net::DefineNetworkTrafficAnnotation("search_prefetch_service", R"(
+// static
+net::NetworkTrafficAnnotationTag
+BaseSearchPrefetchRequest::NetworkAnnotationForPrefetch() {
+  return net::DefineNetworkTrafficAnnotation("search_prefetch_service", R"(
         semantics {
           sender: "Search Prefetch Service"
           description:
@@ -129,6 +130,11 @@ bool BaseSearchPrefetchRequest::StartPrefetchRequest(Profile* profile) {
             }
           }
         })");
+}
+
+bool BaseSearchPrefetchRequest::StartPrefetchRequest(Profile* profile) {
+  net::NetworkTrafficAnnotationTag network_traffic_annotation =
+      NetworkAnnotationForPrefetch();
 
   url::Origin prefetch_origin = url::Origin::Create(prefetch_url_);
 
@@ -137,7 +143,6 @@ bool BaseSearchPrefetchRequest::StartPrefetchRequest(Profile* profile) {
   // navigation speeding and relatively high likelihood of being served to a
   // navigation, the request is relatively high priority.
   resource_request->priority = net::MEDIUM;
-  resource_request->load_flags |= net::LOAD_PREFETCH;
   resource_request->url = prefetch_url_;
   // Search prefetch URL Loaders should check |report_raw_headers| on the
   // intercepted request to clear out the raw headers when |report_raw_headers|

chrome/browser/prefetch/search_prefetch/base_search_prefetch_request.h

@@ -60,6 +60,9 @@ class BaseSearchPrefetchRequest {
   BaseSearchPrefetchRequest& operator=(const BaseSearchPrefetchRequest&) =
       delete;
 
+  // The NTA for any search prefetch request.
+  static net::NetworkTrafficAnnotationTag NetworkAnnotationForPrefetch();
+
   // Starts the network request to prefetch |prefetch_url_|. Sets various fields
   // on a resource request and calls |StartPrefetchRequestInternal()|. Returns
   // |false| if the request is not started (i.e., it would be deferred by
@@ -81,6 +84,9 @@ class BaseSearchPrefetchRequest {
   // Update the status when the relevant search item is clicked in omnibox.
   void MarkPrefetchAsClicked();
 
+  // The URL for the prefetch request.
+  const GURL& prefetch_url() { return prefetch_url_; }
+
   // Whether the prefetch should be served based on |headers|.
   bool CanServePrefetchRequest(
       const scoped_refptr<net::HttpResponseHeaders> headers);

chrome/browser/prefetch/search_prefetch/field_trial_settings.cc

@@ -73,3 +73,8 @@ bool StreamSearchPrefetchResponses() {
   return base::GetFieldTrialParamByFeatureAsBool(
       kSearchPrefetchServicePrefetching, "stream_responses", true);
 }
+
+size_t SearchPrefetchMaxCacheEntries() {
+  return base::GetFieldTrialParamByFeatureAsInt(
+      kSearchPrefetchServicePrefetching, "cache_size", 10);
+}

chrome/browser/prefetch/search_prefetch/field_trial_settings.h

@@ -43,4 +43,8 @@ bool SearchPrefetchShouldCancelUneededInflightRequests();
 // requests.
 bool StreamSearchPrefetchResponses();
 
+// The max number of stored cached prefetch responses. This is stored as a list
+// of navigation URLs to prefetch URLs.
+size_t SearchPrefetchMaxCacheEntries();
+
 #endif  // CHROME_BROWSER_PREFETCH_SEARCH_PREFETCH_FIELD_TRIAL_SETTINGS_H_

chrome/browser/prefetch/search_prefetch/search_prefetch_service.cc

@@ -10,6 +10,7 @@
 #include "base/metrics/histogram_macros.h"
 #include "chrome/browser/content_settings/host_content_settings_map_factory.h"
 #include "chrome/browser/net/prediction_options.h"
+#include "chrome/browser/prefetch/search_prefetch/back_forward_search_prefetch_url_loader.h"
 #include "chrome/browser/prefetch/search_prefetch/field_trial_settings.h"
 #include "chrome/browser/prefetch/search_prefetch/full_body_search_prefetch_request.h"
 #include "chrome/browser/prefetch/search_prefetch/search_prefetch_url_loader.h"
@@ -227,7 +228,8 @@ SearchPrefetchService::GetSearchPrefetchStatusForTesting(
 }
 
 std::unique_ptr<SearchPrefetchURLLoader>
-SearchPrefetchService::TakePrefetchResponse(const GURL& url) {
+SearchPrefetchService::TakePrefetchResponseFromMemoryCache(
+    const GURL& navigation_url) {
   SearchPrefetchServingReasonRecorder recorder;
 
   auto* template_url_service =
@@ -248,15 +250,16 @@ SearchPrefetchService::TakePrefetchResponse(const GURL& url) {
   auto* content_settings =
       HostContentSettingsMapFactory::GetForProfile(profile_);
   if (!content_settings ||
-      content_settings->GetContentSetting(
-          url, url, ContentSettingsType::JAVASCRIPT) == CONTENT_SETTING_BLOCK) {
+      content_settings->GetContentSetting(navigation_url, navigation_url,
+                                          ContentSettingsType::JAVASCRIPT) ==
+          CONTENT_SETTING_BLOCK) {
     recorder.reason_ = SearchPrefetchServingReason::kJavascriptDisabled;
     return nullptr;
   }
 
   base::string16 search_terms;
   template_url_service->GetDefaultSearchProvider()->ExtractSearchTermsFromURL(
-      url, template_url_service->search_terms_data(), &search_terms);
+      navigation_url, template_url_service->search_terms_data(), &search_terms);
 
   if (search_terms.length() == 0) {
     recorder.reason_ = SearchPrefetchServingReason::kNotDefaultSearchWithTerms;
@@ -274,7 +277,7 @@ SearchPrefetchService::TakePrefetchResponse(const GURL& url) {
   // checks should address this by clearing prefetches on user changes to
   // default search, it is paramount to never serve content from one origin to
   // another.
-  if (url::Origin::Create(url) !=
+  if (url::Origin::Create(navigation_url) !=
       url::Origin::Create(iter->second->prefetch_url())) {
     recorder.reason_ =
         SearchPrefetchServingReason::kPrefetchWasForDifferentOrigin;
@@ -302,14 +305,29 @@ SearchPrefetchService::TakePrefetchResponse(const GURL& url) {
   std::unique_ptr<SearchPrefetchURLLoader> response =
       iter->second->TakeSearchPrefetchURLLoader();
 
+  AddCacheEntry(navigation_url, iter->second->prefetch_url());
+
   DeletePrefetch(search_terms);
 
   return response;
 }
 
+std::unique_ptr<SearchPrefetchURLLoader>
+SearchPrefetchService::TakePrefetchResponseFromDiskCache(
+    const GURL& navigation_url) {
+  if (prefetch_cache_.find(navigation_url) == prefetch_cache_.end()) {
+    return nullptr;
+  }
+
+  return std::make_unique<BackForwardSearchPrefetchURLLoader>(
+      profile_, BaseSearchPrefetchRequest::NetworkAnnotationForPrefetch(),
+      prefetch_cache_[navigation_url].first);
+}
+
 void SearchPrefetchService::ClearPrefetches() {
   prefetches_.clear();
   prefetch_expiry_timers_.clear();
+  prefetch_cache_.clear();
 }
 
 void SearchPrefetchService::DeletePrefetch(base::string16 search_terms) {
@@ -418,3 +436,36 @@ void SearchPrefetchService::OnTemplateURLServiceChanged() {
   template_url_service_data_ = template_url_service_data;
   ClearPrefetches();
 }
+
+void SearchPrefetchService::ClearCacheEntry(const GURL& navigation_url) {
+  prefetch_cache_.erase(navigation_url);
+}
+
+void SearchPrefetchService::UpdateServeTime(const GURL& navigation_url) {
+  if (prefetch_cache_.find(navigation_url) == prefetch_cache_.end())
+    return;
+  prefetch_cache_[navigation_url].second = base::Time::Now();
+}
+
+void SearchPrefetchService::AddCacheEntry(const GURL& navigation_url,
+                                          const GURL& prefetch_url) {
+  // TODO(ryansturm): Add prefs support to handle session restore.
+  // https://crbug.com/1162121.
+  prefetch_cache_.emplace(navigation_url,
+                          std::make_pair(prefetch_url, base::Time::Now()));
+
+  if (prefetch_cache_.size() <= SearchPrefetchMaxCacheEntries()) {
+    return;
+  }
+
+  GURL url_to_remove;
+  base::Time earliest_time = base::Time::Now();
+  for (const auto& entry : prefetch_cache_) {
+    base::Time last_used_time = entry.second.second;
+    if (last_used_time < earliest_time) {
+      earliest_time = last_used_time;
+      url_to_remove = entry.first;
+    }
+  }
+  ClearCacheEntry(url_to_remove);
+}

chrome/browser/prefetch/search_prefetch/search_prefetch_service.h

@@ -97,15 +97,30 @@ class SearchPrefetchService : public KeyedService,
   // Clear all prefetches from the service.
   void ClearPrefetches();
 
+  // Clear the disk cache entry for |url|.
+  void ClearCacheEntry(const GURL& navigation_url);
+
+  // Update the last serving time of |url|, so it's eviction priority is
+  // lowered.
+  void UpdateServeTime(const GURL& navigation_url);
+
   // Takes the response from this object if |url| matches a prefetched URL.
-  std::unique_ptr<SearchPrefetchURLLoader> TakePrefetchResponse(
-      const GURL& url);
+  std::unique_ptr<SearchPrefetchURLLoader> TakePrefetchResponseFromMemoryCache(
+      const GURL& navigation_url);
+
+  // Creates a cache loader to serve a cache only response with fallback to
+  // network fetch.
+  std::unique_ptr<SearchPrefetchURLLoader> TakePrefetchResponseFromDiskCache(
+      const GURL& navigation_url);
 
   // Reports the status of a prefetch for a given search term.
   base::Optional<SearchPrefetchStatus> GetSearchPrefetchStatusForTesting(
       base::string16 search_terms);
 
  private:
+  // Records a cache entry for a navigation that is being served.
+  void AddCacheEntry(const GURL& navigation_url, const GURL& prefetch_url);
+
   // Removes the prefetch and prefetch timers associated with |search_terms|.
   void DeletePrefetch(base::string16 search_terms);
 
@@ -141,6 +156,11 @@ class SearchPrefetchService : public KeyedService,
       observer_{this};
 
   Profile* profile_;
+
+  // A map of previously handled URLs that allows certain navigations to be
+  // served from cache. The value is the prefetch URL in cache and the latest
+  // serving time of the response.
+  std::map<GURL, std::pair<GURL, base::Time>> prefetch_cache_;
 };
 
 #endif  // CHROME_BROWSER_PREFETCH_SEARCH_PREFETCH_SEARCH_PREFETCH_SERVICE_H_

chrome/browser/prefetch/search_prefetch/search_prefetch_url_loader_interceptor.cc

@@ -20,6 +20,7 @@
 #include "content/public/browser/render_frame_host.h"
 #include "content/public/browser/storage_partition.h"
 #include "content/public/browser/web_contents.h"
+#include "net/base/load_flags.h"
 
 SearchPrefetchURLLoaderInterceptor::SearchPrefetchURLLoaderInterceptor(
     int frame_tree_node_id)
@@ -56,7 +57,15 @@ SearchPrefetchURLLoaderInterceptor::MaybeCreateLoaderForRequest(
   if (!service)
     return nullptr;
 
-  return service->TakePrefetchResponse(tentative_resource_request.url);
+  auto loader = service->TakePrefetchResponseFromMemoryCache(
+      tentative_resource_request.url);
+  if (loader)
+    return loader;
+  if (tentative_resource_request.load_flags & net::LOAD_SKIP_CACHE_VALIDATION) {
+    return service->TakePrefetchResponseFromDiskCache(
+        tentative_resource_request.url);
+  }
+  return nullptr;
 }
 
 void SearchPrefetchURLLoaderInterceptor::MaybeCreateLoader(