Harden User-Agent code for Prefetch Proxy's prefetches

Mostly adds testing to ensure the UA header is set correctly, and uses
the content API for the UA string instead.

Change-Id: Id54ec973dc6837b92aa19cde3149e1097423374d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521351
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Auto-Submit: Robert Ogden <robertogden@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824555}

chrome/browser/prefetch/prefetch_proxy/prefetch_proxy_browsertest.cc

@@ -70,6 +70,7 @@
 #include "components/security_interstitials/content/ssl_cert_reporter.h"
 #include "components/ukm/test_ukm_recorder.h"
 #include "components/variations/variations_params_manager.h"
+#include "components/version_info/version_info.h"
 #include "content/public/browser/browser_task_traits.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/navigation_controller.h"
@@ -78,8 +79,10 @@
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/service_worker_context.h"
 #include "content/public/browser/storage_partition.h"
+#include "content/public/common/content_switches.h"
 #include "content/public/common/network_service_util.h"
 #include "content/public/common/page_type.h"
+#include "content/public/common/user_agent.h"
 #include "content/public/test/browser_test.h"
 #include "content/public/test/browser_test_base.h"
 #include "content/public/test/browser_test_utils.h"
@@ -681,6 +684,28 @@ class PrefetchProxyBrowserTest
                                      });
   }
 
+  // Uses the url's path to match requests since the host from
+  // EmbeddedTestServer is always 127.0.0.1.
+  void VerifyOriginRequestsAreIsolated(const std::set<std::string>& paths) {
+    size_t verified_url_count = 0;
+    for (const auto& request : origin_server_requests()) {
+      const GURL& url = request.GetURL();
+      if (paths.find(url.path()) == paths.end()) {
+        continue;
+      }
+
+      SCOPED_TRACE(request.GetURL().spec());
+      EXPECT_EQ(request.headers.find("user-agent")->second,
+                content::GetFrozenUserAgent(
+                    base::CommandLine::ForCurrentProcess()->HasSwitch(
+                        switches::kUseMobileUserAgent),
+                    version_info::GetMajorVersionNumber()));
+      EXPECT_EQ(request.headers.find("purpose")->second, "prefetch");
+      verified_url_count++;
+    }
+    EXPECT_EQ(paths.size(), verified_url_count);
+  }
+
   size_t OriginServerRequestCount() const {
     base::RunLoop().RunUntilIdle();
     return origin_server_request_count_;
@@ -715,6 +740,8 @@ class PrefetchProxyBrowserTest
     if (request.GetURL().spec().find("favicon") != std::string::npos)
       return nullptr;
 
+    SCOPED_TRACE(request.GetURL().spec());
+
     content::GetUIThreadTaskRunner({})->PostTask(
         FROM_HERE,
         base::BindOnce(
@@ -1169,6 +1196,8 @@ IN_PROC_BROWSER_TEST_F(PrefetchProxyBrowserTest,
   EXPECT_EQ(base::UTF8ToUTF16("Title Of Awesomeness"),
             GetWebContents()->GetTitle());
 
+  VerifyOriginRequestsAreIsolated({prefetch_url.path()});
+
   // The origin server should not have served this request.
   EXPECT_EQ(starting_origin_request_count, OriginServerRequestCount());
 }
@@ -1229,6 +1258,12 @@ IN_PROC_BROWSER_TEST_F(PrefetchProxyBrowserTest,
   ui_test_utils::NavigateToURL(browser(), eligible_link_2);
   base::RunLoop().RunUntilIdle();
 
+  VerifyOriginRequestsAreIsolated({
+      eligible_link_1.path(),
+      eligible_link_2.path(),
+      eligible_link_3.path(),
+  });
+
   using UkmEntry = ukm::TestUkmRecorder::HumanReadableUkmEntry;
   auto expected_entries = std::vector<UkmEntry>{
       // eligible_link_1
@@ -2621,6 +2656,11 @@ IN_PROC_BROWSER_TEST_F(PrefetchProxyWithNSPBrowserTest,
   EXPECT_FALSE(found_nsp_mainframe);
   EXPECT_FALSE(found_image);
 
+  VerifyOriginRequestsAreIsolated({
+      "/prefetch/prefetch_proxy/prefetch.js",
+      eligible_link.path(),
+  });
+
   // Verify the resource load was reported to the subresource manager.
   PrefetchProxyService* service =
       PrefetchProxyServiceFactory::GetForProfile(browser()->profile());

chrome/browser/prefetch/prefetch_proxy/prefetch_proxy_tab_helper.cc

@@ -8,6 +8,7 @@
 
 #include "base/barrier_closure.h"
 #include "base/bind.h"
+#include "base/command_line.h"
 #include "base/feature_list.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/histogram_functions.h"
@@ -35,6 +36,7 @@
 #include "components/prefs/pref_service.h"
 #include "components/prerender/browser/prerender_manager.h"
 #include "components/search_engines/template_url_service.h"
+#include "components/version_info/version_info.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/navigation_handle.h"
 #include "content/public/browser/network_service_instance.h"
@@ -44,6 +46,8 @@
 #include "content/public/browser/storage_partition.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/common/content_constants.h"
+#include "content/public/common/content_switches.h"
+#include "content/public/common/user_agent.h"
 #include "mojo/public/cpp/bindings/self_owned_receiver.h"
 #include "net/base/isolation_info.h"
 #include "net/base/load_flags.h"
@@ -700,6 +704,9 @@ void PrefetchProxyTabHelper::StartSinglePrefetch() {
   request->load_flags = net::LOAD_DISABLE_CACHE | net::LOAD_PREFETCH;
   request->credentials_mode = network::mojom::CredentialsMode::kInclude;
   request->headers.SetHeader(content::kCorsExemptPurposeHeaderName, "prefetch");
+  // Remove the user agent header if it was set so that the network context's
+  // default is used.
+  request->headers.RemoveHeader("User-Agent");
   request->trusted_params = trusted_params;
   request->site_for_cookies = trusted_params.isolation_info.site_for_cookies();
 
@@ -1373,7 +1380,10 @@ void PrefetchProxyTabHelper::CreateIsolatedURLLoaderFactory() {
 
   auto context_params = network::mojom::NetworkContextParams::New();
   context_params->context_name = "PrefetchProxy";
-  context_params->user_agent = ::GetUserAgent();
+  context_params->user_agent = content::GetFrozenUserAgent(
+      base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kUseMobileUserAgent),
+      version_info::GetMajorVersionNumber());
   context_params->accept_language = net::HttpUtil::GenerateAcceptLanguageHeader(
       profile_->GetPrefs()->GetString(language::prefs::kAcceptLanguages));
   context_params->initial_custom_proxy_config =