Reland "Port policy::UploadJobImpl to network::SimpleURLLoader"

This reverts commit b624551f.

Reason for revert: Reverting this change broke the tree because of a patch that depends on it. Since the test is only flaky fixing the tree is better than causing more disturbance by reverting more changes.

Original change's description:
> Revert "Port policy::UploadJobImpl to network::SimpleURLLoader"
> 
> This reverts commit 581330a9.
> 
> Reason for revert: SimpleURLLoaderTest.OnUploadProgressCallback/3 is flaky
> 
> Original change's description:
> > Port policy::UploadJobImpl to network::SimpleURLLoader
> > 
> > This change ports UploadJobImpl from net::URLFetcher to SimpleURLLoader.
> > 
> > Since this request does not make use of the response a new method has
> > been added to SimpleURLLoader, DownloadToNull. This download mode still
> > reads the response body from the network but does not save it anywhere.
> > This is useful for requests which upload data and would otherwise have
> > to specify an arbitrary |max_body_size|. A maximum may still be set if
> > the caller wants to limit the amount of data transferred over the
> > network.
> > 
> > Bug: 773295
> > Cq-Include-Trybots: luci.chromium.try:linux_mojo
> > Change-Id: Iee1fdc6f7406066ced8c91122e22cd51ddcb1c5f
> > Reviewed-on: https://chromium-review.googlesource.com/1161551
> > Commit-Queue: Reilly Grant <reillyg@chromium.org>
> > Reviewed-by: Matt Menke <mmenke@chromium.org>
> > Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#581060}
> 
> TBR=pastarmovj@chromium.org,reillyg@chromium.org,mmenke@chromium.org
> 
> Change-Id: Ica09c85a12861d35efbdfd9a882d137bac6b9e56
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 773295, 872023
> Cq-Include-Trybots: luci.chromium.try:linux_mojo
> Reviewed-on: https://chromium-review.googlesource.com/1166288
> Reviewed-by: Reilly Grant <reillyg@chromium.org>
> Commit-Queue: Reilly Grant <reillyg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#581389}

TBR=pastarmovj@chromium.org,reillyg@chromium.org,mmenke@chromium.org

Change-Id: I793ab6c8c22c5bec97ef853f520dc506809970cb
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 773295, 872023
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Reviewed-on: https://chromium-review.googlesource.com/1166301Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581394}

chrome/browser/chromeos/policy/remote_commands/screenshot_delegate.cc

@@ -53,8 +53,6 @@ std::unique_ptr<UploadJob> ScreenshotDelegate::CreateUploadJob(
   chromeos::DeviceOAuth2TokenService* device_oauth2_token_service =
       chromeos::DeviceOAuth2TokenServiceFactory::Get();
 
-  scoped_refptr<net::URLRequestContextGetter> system_request_context =
-      g_browser_process->system_request_context();
   std::string robot_account_id =
       device_oauth2_token_service->GetRobotAccountId();
 
@@ -80,7 +78,7 @@ std::unique_ptr<UploadJob> ScreenshotDelegate::CreateUploadJob(
       )");
   return std::unique_ptr<UploadJob>(new UploadJobImpl(
       upload_url, robot_account_id, device_oauth2_token_service,
-      system_request_context, delegate,
+      g_browser_process->shared_url_loader_factory(), delegate,
       base::WrapUnique(new UploadJobImpl::RandomMimeBoundaryGenerator),
       traffic_annotation, base::ThreadTaskRunnerHandle::Get()));
 }

chrome/browser/chromeos/policy/system_log_uploader.cc

@@ -27,6 +27,7 @@
 #include "components/policy/core/browser/browser_policy_connector.h"
 #include "components/user_manager/user_manager.h"
 #include "net/http/http_request_headers.h"
+#include "services/network/public/cpp/shared_url_loader_factory.h"
 
 namespace policy {
 
@@ -144,8 +145,6 @@ std::unique_ptr<UploadJob> SystemLogDelegate::CreateUploadJob(
   chromeos::DeviceOAuth2TokenService* device_oauth2_token_service =
       chromeos::DeviceOAuth2TokenServiceFactory::Get();
 
-  scoped_refptr<net::URLRequestContextGetter> system_request_context =
-      g_browser_process->system_request_context();
   std::string robot_account_id =
       device_oauth2_token_service->GetRobotAccountId();
 
@@ -173,7 +172,7 @@ std::unique_ptr<UploadJob> SystemLogDelegate::CreateUploadJob(
       )");
   return std::make_unique<UploadJobImpl>(
       upload_url, robot_account_id, device_oauth2_token_service,
-      system_request_context, delegate,
+      g_browser_process->shared_url_loader_factory(), delegate,
       std::make_unique<UploadJobImpl::RandomMimeBoundaryGenerator>(),
       traffic_annotation, task_runner_);
 }

chrome/browser/chromeos/policy/upload_job_impl.cc

@@ -19,7 +19,8 @@
 #include "net/base/mime_util.h"
 #include "net/http/http_status_code.h"
 #include "net/traffic_annotation/network_traffic_annotation.h"
-#include "net/url_request/url_request_status.h"
+#include "services/network/public/cpp/shared_url_loader_factory.h"
+#include "services/network/public/cpp/simple_url_loader.h"
 
 namespace policy {
 
@@ -27,7 +28,7 @@ namespace {
 
 // Format for bearer tokens in HTTP requests to access OAuth 2.0 protected
 // resources.
-const char kAuthorizationHeaderFormat[] = "Authorization: Bearer %s";
+const char kAuthorizationHeaderFormat[] = "Bearer %s";
 
 // Value the "Content-Type" field will be set to in the POST request.
 const char kUploadContentType[] = "multipart/form-data";
@@ -151,7 +152,7 @@ UploadJobImpl::UploadJobImpl(
     const GURL& upload_url,
     const std::string& account_id,
     OAuth2TokenService* token_service,
-    scoped_refptr<net::URLRequestContextGetter> url_context_getter,
+    scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
     Delegate* delegate,
     std::unique_ptr<MimeBoundaryGenerator> boundary_generator,
     net::NetworkTrafficAnnotationTag traffic_annotation,
@@ -160,7 +161,7 @@ UploadJobImpl::UploadJobImpl(
       upload_url_(upload_url),
       account_id_(account_id),
       token_service_(token_service),
-      url_context_getter_(url_context_getter),
+      url_loader_factory_(std::move(url_loader_factory)),
       delegate_(delegate),
       boundary_generator_(std::move(boundary_generator)),
       traffic_annotation_(traffic_annotation),
@@ -169,7 +170,7 @@ UploadJobImpl::UploadJobImpl(
       task_runner_(task_runner),
       weak_factory_(this) {
   DCHECK(token_service_);
-  DCHECK(url_context_getter_);
+  DCHECK(url_loader_factory_);
   DCHECK(delegate_);
   SYSLOG(INFO) << "Upload job created.";
   if (!upload_url_.is_valid()) {
@@ -299,7 +300,7 @@ bool UploadJobImpl::SetUpMultipart() {
   return true;
 }
 
-void UploadJobImpl::CreateAndStartURLFetcher(const std::string& access_token) {
+void UploadJobImpl::CreateAndStartURLLoader(const std::string& access_token) {
   // Ensure that the content has been prepared and the upload url is valid.
   DCHECK_EQ(PREPARING_CONTENT, state_);
   SYSLOG(INFO) << "Starting URL fetcher.";
@@ -308,13 +309,20 @@ void UploadJobImpl::CreateAndStartURLFetcher(const std::string& access_token) {
   content_type.append("; boundary=");
   content_type.append(*mime_boundary_.get());
 
-  upload_fetcher_ = net::URLFetcher::Create(upload_url_, net::URLFetcher::POST,
-                                            this, traffic_annotation_);
-  upload_fetcher_->SetRequestContext(url_context_getter_.get());
-  upload_fetcher_->SetUploadData(content_type, *post_data_);
-  upload_fetcher_->AddExtraRequestHeader(
+  auto resource_request = std::make_unique<network::ResourceRequest>();
+  resource_request->method = "POST";
+  resource_request->url = upload_url_;
+  resource_request->headers.SetHeader(
+      net::HttpRequestHeaders::kAuthorization,
       base::StringPrintf(kAuthorizationHeaderFormat, access_token.c_str()));
-  upload_fetcher_->Start();
+
+  url_loader_ = network::SimpleURLLoader::Create(std::move(resource_request),
+                                                 traffic_annotation_);
+  url_loader_->AttachStringForUpload(*post_data_, content_type);
+  url_loader_->DownloadHeadersOnly(
+      url_loader_factory_.get(),
+      base::BindOnce(&UploadJobImpl::OnURLLoadComplete,
+                     base::Unretained(this)));
 }
 
 void UploadJobImpl::StartUpload() {
@@ -326,7 +334,7 @@ void UploadJobImpl::StartUpload() {
     state_ = ERROR;
     return;
   }
-  CreateAndStartURLFetcher(access_token_);
+  CreateAndStartURLLoader(access_token_);
   state_ = UPLOADING;
 }
 
@@ -356,7 +364,7 @@ void UploadJobImpl::OnGetTokenFailure(
 
 void UploadJobImpl::HandleError(ErrorCode error_code) {
   retry_++;
-  upload_fetcher_.reset();
+  url_loader_.reset();
 
   SYSLOG(ERROR) << "Upload failed, error code: " << error_code;
 
@@ -397,35 +405,32 @@ void UploadJobImpl::HandleError(ErrorCode error_code) {
   }
 }
 
-void UploadJobImpl::OnURLFetchComplete(const net::URLFetcher* source) {
-  DCHECK_EQ(upload_fetcher_.get(), source);
+void UploadJobImpl::OnURLLoadComplete(
+    scoped_refptr<net::HttpResponseHeaders> headers) {
   DCHECK_EQ(UPLOADING, state_);
+
   SYSLOG(INFO) << "URL fetch completed.";
-  const net::URLRequestStatus& status = source->GetStatus();
-  if (!status.is_success()) {
-    SYSLOG(ERROR) << "URLRequestStatus error " << status.error();
+  std::unique_ptr<network::SimpleURLLoader> url_loader = std::move(url_loader_);
+
+  if (!headers) {
+    SYSLOG(ERROR) << "SimpleURLLoader error " << url_loader->NetError();
     HandleError(NETWORK_ERROR);
-  } else {
-    const int response_code = source->GetResponseCode();
-    if (response_code == net::HTTP_OK) {
+  } else if (headers->response_code() == net::HTTP_OK) {
     // Successful upload
-      upload_fetcher_.reset();
     access_token_.clear();
     post_data_.reset();
     state_ = SUCCESS;
-      UMA_HISTOGRAM_EXACT_LINEAR(
-          kUploadJobSuccessHistogram, retry_,
+    UMA_HISTOGRAM_EXACT_LINEAR(kUploadJobSuccessHistogram, retry_,
                                static_cast<int>(UploadJobSuccess::REQUEST_MAX));
     delegate_->OnSuccess();
-    } else if (response_code == net::HTTP_UNAUTHORIZED) {
+  } else if (headers->response_code() == net::HTTP_UNAUTHORIZED) {
     SYSLOG(ERROR) << "Unauthorized request.";
     HandleError(AUTHENTICATION_ERROR);
   } else {
     SYSLOG(ERROR) << "POST request failed with HTTP status code "
-                    << response_code << ".";
+                  << headers->response_code() << ".";
     HandleError(SERVER_ERROR);
   }
-  }
 }
 
 }  // namespace policy

chrome/browser/chromeos/policy/upload_job_impl.h

@@ -15,23 +15,28 @@
 #include "base/threading/thread_checker.h"
 #include "chrome/browser/chromeos/policy/upload_job.h"
 #include "google_apis/gaia/oauth2_token_service.h"
-#include "net/url_request/url_fetcher.h"
-#include "net/url_request/url_fetcher_delegate.h"
-#include "net/url_request/url_request_context_getter.h"
+#include "net/traffic_annotation/network_traffic_annotation.h"
 #include "url/gurl.h"
 
 namespace base {
 class SequencedTaskRunner;
 }
 
+namespace net {
+class HttpResponseHeaders;
+}
+
+namespace network {
+class SharedURLLoaderFactory;
+class SimpleURLLoader;
+}  // namespace network
+
 namespace policy {
 
 // This implementation of UploadJob uses the OAuth2TokenService to acquire
 // access tokens for the device management (cloud-based policy) server scope and
-// uses a URLFetcher to upload data to the specified upload url.
-class UploadJobImpl : public UploadJob,
-                      public OAuth2TokenService::Consumer,
-                      public net::URLFetcherDelegate {
+// uses a SimpleURLLoader to upload data to the specified upload url.
+class UploadJobImpl : public UploadJob, public OAuth2TokenService::Consumer {
  public:
   // UploadJobImpl uses a MimeBoundaryGenerator to generate strings which
   // mark the boundaries between data segments.
@@ -56,10 +61,11 @@ class UploadJobImpl : public UploadJob,
 
   // |task_runner| must belong to the same thread from which the constructor and
   // all the public methods are called.
-  UploadJobImpl(const GURL& upload_url,
+  UploadJobImpl(
+      const GURL& upload_url,
       const std::string& account_id,
       OAuth2TokenService* token_service,
-                scoped_refptr<net::URLRequestContextGetter> url_context_getter,
+      scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
       Delegate* delegate,
       std::unique_ptr<MimeBoundaryGenerator> boundary_generator,
       net::NetworkTrafficAnnotationTag traffic_annotation,
@@ -103,15 +109,15 @@ class UploadJobImpl : public UploadJob,
   void OnGetTokenFailure(const OAuth2TokenService::Request* request,
                          const GoogleServiceAuthError& error) override;
 
-  // net::URLFetcherDelegate:
-  void OnURLFetchComplete(const net::URLFetcher* source) override;
+  // Called when the SimpleURLLoader is finished.
+  void OnURLLoadComplete(scoped_refptr<net::HttpResponseHeaders> headers);
 
   void HandleError(ErrorCode errorCode);
 
   // Requests an access token for the upload scope.
   void RequestAccessToken();
 
-  // Dispatches POST request to URLFetcher.
+  // Dispatches POST request.
   void StartUpload();
 
   // Constructs the body of the POST request by concatenating the
@@ -122,9 +128,9 @@ class UploadJobImpl : public UploadJob,
   // an error, clears |post_data_| and |mime_boundary_| and returns false.
   bool SetUpMultipart();
 
-  // Assembles the request and starts the URLFetcher. Fails if another upload
-  // is still in progress or the content was not successfully encoded.
-  void CreateAndStartURLFetcher(const std::string& access_token);
+  // Assembles the request and starts the SimpleURLLoader. Fails if another
+  // upload is still in progress or the content was not successfully encoded.
+  void CreateAndStartURLLoader(const std::string& access_token);
 
   // The URL to which the POST request should be directed.
   const GURL upload_url_;
@@ -135,8 +141,8 @@ class UploadJobImpl : public UploadJob,
   // The token service used to retrieve the access token.
   OAuth2TokenService* const token_service_;
 
-  // This is used to initialize the net::URLFetcher object.
-  const scoped_refptr<net::URLRequestContextGetter> url_context_getter_;
+  // This is used to initialize the network::SimpleURLLoader object.
+  const scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory_;
 
   // The delegate to be notified of events.
   Delegate* const delegate_;
@@ -169,7 +175,7 @@ class UploadJobImpl : public UploadJob,
   std::string access_token_;
 
   // Helper to upload the data.
-  std::unique_ptr<net::URLFetcher> upload_fetcher_;
+  std::unique_ptr<network::SimpleURLLoader> url_loader_;
 
   // The data chunks to be uploaded.
   std::vector<std::unique_ptr<DataSegment>> data_segments_;

chrome/browser/chromeos/policy/upload_job_unittest.cc

@@ -27,8 +27,7 @@
 #include "net/test/embedded_test_server/http_request.h"
 #include "net/test/embedded_test_server/http_response.h"
 #include "net/traffic_annotation/network_traffic_annotation_test_helper.h"
-#include "net/url_request/url_request_test_util.h"
-#include "services/network/public/cpp/shared_url_loader_factory.h"
+#include "services/network/test/test_shared_url_loader_factory.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace policy {
@@ -183,8 +182,8 @@ class UploadJobTestBase : public testing::Test, public UploadJob::Delegate {
 
   // testing::Test:
   void SetUp() override {
-    request_context_getter_ = new net::TestURLRequestContextGetter(
-        base::ThreadTaskRunnerHandle::Get());
+    url_loader_factory_ =
+        base::MakeRefCounted<network::TestSharedURLLoaderFactory>();
     oauth2_service_.AddAccount("robot@gmail.com");
     ASSERT_TRUE(test_server_.Start());
     // Set retry delay to prevent timeouts
@@ -201,9 +200,9 @@ class UploadJobTestBase : public testing::Test, public UploadJob::Delegate {
       std::unique_ptr<UploadJobImpl::MimeBoundaryGenerator>
           mime_boundary_generator) {
     std::unique_ptr<UploadJob> upload_job(new UploadJobImpl(
-        GetServerURL(), kRobotAccountId, &oauth2_service_,
-        request_context_getter_.get(), this, std::move(mime_boundary_generator),
-        TRAFFIC_ANNOTATION_FOR_TESTS, base::ThreadTaskRunnerHandle::Get()));
+        GetServerURL(), kRobotAccountId, &oauth2_service_, url_loader_factory_,
+        this, std::move(mime_boundary_generator), TRAFFIC_ANNOTATION_FOR_TESTS,
+        base::ThreadTaskRunnerHandle::Get()));
 
     std::map<std::string, std::string> header_entries;
     header_entries.insert(std::make_pair(kCustomField1, "CUSTOM1"));
@@ -220,7 +219,7 @@ class UploadJobTestBase : public testing::Test, public UploadJob::Delegate {
   content::TestBrowserThreadBundle test_browser_thread_bundle_;
   base::RunLoop run_loop_;
   net::EmbeddedTestServer test_server_;
-  scoped_refptr<net::TestURLRequestContextGetter> request_context_getter_;
+  scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory_;
   MockOAuth2TokenService oauth2_service_;
 
   std::unique_ptr<UploadJob::ErrorCode> expected_error_;

services/network/public/cpp/simple_url_loader.cc

@@ -188,6 +188,8 @@ class SimpleURLLoaderImpl : public SimpleURLLoader,
   void DownloadToStringOfUnboundedSizeUntilCrashAndDie(
       mojom::URLLoaderFactory* url_loader_factory,
       BodyAsStringCallback body_as_string_callback) override;
+  void DownloadHeadersOnly(mojom::URLLoaderFactory* url_loader_factory,
+                           HeadersOnlyCallback headers_only_callback) override;
   void DownloadToFile(
       mojom::URLLoaderFactory* url_loader_factory,
       DownloadToFileCompleteCallback download_to_file_complete_callback,
@@ -625,6 +627,58 @@ class SaveToStringBodyHandler : public BodyHandler,
   DISALLOW_COPY_AND_ASSIGN(SaveToStringBodyHandler);
 };
 
+// BodyHandler that discards the response body.
+class HeadersOnlyBodyHandler : public BodyHandler, public BodyReader::Delegate {
+ public:
+  HeadersOnlyBodyHandler(
+      SimpleURLLoaderImpl* simple_url_loader,
+      SimpleURLLoader::HeadersOnlyCallback headers_only_callback)
+      : BodyHandler(simple_url_loader),
+        headers_only_callback_(std::move(headers_only_callback)) {}
+
+  ~HeadersOnlyBodyHandler() override {}
+
+  // BodyHandler implementation
+  void OnStartLoadingResponseBody(
+      mojo::ScopedDataPipeConsumerHandle body_data_pipe) override {
+    // TODO(crbug.com/871420): The request can be completed at this point
+    // however that requires more changes to SimpleURLLoader as OnComplete()
+    // will not have been called yet.
+    DCHECK(!body_reader_);
+    body_reader_ =
+        std::make_unique<BodyReader>(this, std::numeric_limits<int64_t>::max());
+    body_reader_->Start(std::move(body_data_pipe));
+  }
+
+  void NotifyConsumerOfCompletion(bool destroy_results) override {
+    body_reader_.reset();
+    std::move(headers_only_callback_)
+        .Run(simple_url_loader()->ResponseInfo()
+                 ? simple_url_loader()->ResponseInfo()->headers
+                 : nullptr);
+  }
+
+  void PrepareToRetry(base::OnceClosure retry_callback) override {
+    body_reader_.reset();
+    std::move(retry_callback).Run();
+  }
+
+ private:
+  // BodyReader::Delegate implementation
+  net::Error OnDataRead(uint32_t length, const char* data) override {
+    return net::OK;
+  }
+
+  void OnDone(net::Error error, int64_t total_bytes) override {
+    simple_url_loader()->OnBodyHandlerDone(error, total_bytes);
+  }
+
+  SimpleURLLoader::HeadersOnlyCallback headers_only_callback_;
+  std::unique_ptr<BodyReader> body_reader_;
+
+  DISALLOW_COPY_AND_ASSIGN(HeadersOnlyBodyHandler);
+};
+
 // BodyHandler implementation for saving the response to a file
 class SaveToFileBodyHandler : public BodyHandler {
  public:
@@ -1061,6 +1115,14 @@ void SimpleURLLoaderImpl::DownloadToStringOfUnboundedSizeUntilCrashAndDie(
   Start(url_loader_factory);
 }
 
+void SimpleURLLoaderImpl::DownloadHeadersOnly(
+    mojom::URLLoaderFactory* url_loader_factory,
+    HeadersOnlyCallback headers_only_callback) {
+  body_handler_ = std::make_unique<HeadersOnlyBodyHandler>(
+      this, std::move(headers_only_callback));
+  Start(url_loader_factory);
+}
+
 void SimpleURLLoaderImpl::DownloadToFile(
     mojom::URLLoaderFactory* url_loader_factory,
     DownloadToFileCompleteCallback download_to_file_complete_callback,
@@ -1246,6 +1308,7 @@ void SimpleURLLoaderImpl::FinishWithResult(int net_error) {
 
   request_state_->finished = true;
   request_state_->net_error = net_error;
+
   // If it's a partial download or an error was received, erase the body.
   bool destroy_results =
       request_state_->net_error != net::OK && !allow_partial_results_;
@@ -1311,7 +1374,6 @@ void SimpleURLLoaderImpl::Retry() {
   url_loader_.reset();
 
   request_state_ = std::make_unique<RequestState>();
-
   body_handler_->PrepareToRetry(base::BindOnce(
       &SimpleURLLoaderImpl::StartRequest, weak_ptr_factory_.GetWeakPtr(),
       url_loader_factory_ptr_.get()));

services/network/public/cpp/simple_url_loader.h

@@ -18,11 +18,15 @@
 
 class GURL;
 
+template <class T>
+class scoped_refptr;
+
 namespace base {
 class FilePath;
 }
 
 namespace net {
+class HttpResponseHeaders;
 struct NetworkTrafficAnnotationTag;
 struct RedirectInfo;
 }  // namespace net
@@ -85,8 +89,14 @@ class COMPONENT_EXPORT(NETWORK_CPP) SimpleURLLoader {
   using BodyAsStringCallback =
       base::OnceCallback<void(std::unique_ptr<std::string> response_body)>;
 
-  // Callback used when download the response body to a file. On failure, |path|
-  // will be empty. It is safe to delete the SimpleURLLoader during the
+  // Callback used when ignoring the response body. |headers| are the received
+  // HTTP headers, or nullptr if none were received. It is safe to delete the
+  // SimpleURLLoader during the callback.
+  using HeadersOnlyCallback =
+      base::OnceCallback<void(scoped_refptr<net::HttpResponseHeaders> headers)>;
+
+  // Callback used when downloading the response body to a file. On failure,
+  // |path| will be empty. It is safe to delete the SimpleURLLoader during the
   // callback.
   using DownloadToFileCompleteCallback =
       base::OnceCallback<void(base::FilePath path)>;
@@ -120,7 +130,7 @@ class COMPONENT_EXPORT(NETWORK_CPP) SimpleURLLoader {
 
   virtual ~SimpleURLLoader();
 
-  // Starts the request using |network_context|. The SimpleURLLoader will
+  // Starts the request using |url_loader_factory|. The SimpleURLLoader will
   // accumulate all downloaded data in an in-memory string of bounded size. If
   // |max_body_size| is exceeded, the request will fail with
   // net::ERR_INSUFFICIENT_RESOURCES. |max_body_size| must be no greater than 1
@@ -145,6 +155,14 @@ class COMPONENT_EXPORT(NETWORK_CPP) SimpleURLLoader {
       mojom::URLLoaderFactory* url_loader_factory,
       BodyAsStringCallback body_as_string_callback) = 0;
 
+  // Starts the request using |url_loader_factory|. The SimpleURLLoader will
+  // discard the response body as it is received and |headers_only_callback|
+  // will be invoked on completion. It is safe to delete the SimpleURLLoader in
+  // this callback.
+  virtual void DownloadHeadersOnly(
+      mojom::URLLoaderFactory* url_loader_factory,
+      HeadersOnlyCallback headers_only_callback) = 0;
+
   // SimpleURLLoader will download the entire response to a file at the
   // specified path. File I/O will happen on another sequence, so it's safe to
   // use this on any sequence.