Use a PassKey to restrict access to URLRequest's ctor

This allows us to make the URLRequest ctor public (to use
std::make_unique instead of new & base::WrapUnique) without allowing
any callers outside of URLRequestContext. It also allows us to remove
the `friend` directive.

Change-Id: I2d0ed2042e7a17246c736510d7d9315827e66d6c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4152592
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Auto-Submit: Chris Fredrickson <cfredric@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1090970}

net/url_request/url_request.cc

@@ -15,6 +15,7 @@
 #include "base/strings/utf_string_conversions.h"
 #include "base/synchronization/lock.h"
 #include "base/task/single_thread_task_runner.h"
+#include "base/types/pass_key.h"
 #include "base/values.h"
 #include "net/base/auth.h"
 #include "net/base/io_buffer.h"
@@ -574,7 +575,8 @@ void URLRequest::Start() {
 
 ///////////////////////////////////////////////////////////////////////////////
 
-URLRequest::URLRequest(const GURL& url,
+URLRequest::URLRequest(base::PassKey<URLRequestContext> pass_key,
+                       const GURL& url,
                        RequestPriority priority,
                        Delegate* delegate,
                        const URLRequestContext* context,

net/url_request/url_request.h

@@ -18,6 +18,7 @@
 #include "base/supports_user_data.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/time.h"
+#include "base/types/pass_key.h"
 #include "net/base/auth.h"
 #include "net/base/completion_repeating_callback.h"
 #include "net/base/idempotency.h"
@@ -206,6 +207,16 @@ class NET_EXPORT URLRequest : public base::SupportsUserData {
     virtual ~Delegate() = default;
   };
 
+  // URLRequests are always created by calling URLRequestContext::CreateRequest.
+  URLRequest(base::PassKey<URLRequestContext> pass_key,
+             const GURL& url,
+             RequestPriority priority,
+             Delegate* delegate,
+             const URLRequestContext* context,
+             NetworkTrafficAnnotationTag traffic_annotation,
+             bool is_for_websockets,
+             absl::optional<net::NetLogSource> net_log_source);
+
   URLRequest(const URLRequest&) = delete;
   URLRequest& operator=(const URLRequest&) = delete;
 
@@ -861,21 +872,11 @@ class NET_EXPORT URLRequest : public base::SupportsUserData {
 
  private:
   friend class URLRequestJob;
-  friend class URLRequestContext;
 
   // For testing purposes.
   // TODO(maksims): Remove this.
   friend class TestNetworkDelegate;
 
-  // URLRequests are always created by calling URLRequestContext::CreateRequest.
-  URLRequest(const GURL& url,
-             RequestPriority priority,
-             Delegate* delegate,
-             const URLRequestContext* context,
-             NetworkTrafficAnnotationTag traffic_annotation,
-             bool is_for_websockets,
-             absl::optional<net::NetLogSource> net_log_source);
-
   // Resumes or blocks a request paused by the NetworkDelegate::OnBeforeRequest
   // handler. If |blocked| is true, the request is blocked and an error page is
   // returned indicating so. This should only be called after Start is called

net/url_request/url_request_context.cc

@@ -13,6 +13,7 @@
 #include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/string_util.h"
+#include "base/types/pass_key.h"
 #include "build/build_config.h"
 #include "build/chromeos_buildflags.h"
 #include "net/base/http_user_agent_settings.h"
@@ -125,9 +126,9 @@ std::unique_ptr<URLRequest> URLRequestContext::CreateRequest(
     NetworkTrafficAnnotationTag traffic_annotation,
     bool is_for_websockets,
     const absl::optional<net::NetLogSource> net_log_source) const {
-  return base::WrapUnique(new URLRequest(url, priority, delegate, this,
-                                         traffic_annotation, is_for_websockets,
-                                         net_log_source));
+  return std::make_unique<URLRequest>(
+      base::PassKey<URLRequestContext>(), url, priority, delegate, this,
+      traffic_annotation, is_for_websockets, net_log_source);
 }
 
 void URLRequestContext::AssertNoURLRequests() const {