[MIX-DL] Fix blob: URL handling and clarify console messages

This CL fixes a bug wherein the final URL in a redirect chain was
considered as part of the middle of the redirect chain. This resulted in
two seemingly-unrelated bugs:
 * The console message always said that blocked downloads were
   "redirected through" an insecure URL, even if there were no
   redirects/the redirects were all secure.
 * file:// and blob:// URLs were considered insecure, even when you got
   there through secure means, and even though we had tried to
   special-case them.

The only non-test change in this CL is to exclude the last URL in the
redirect chain when considering redirects, since the last URL in the
chain is always the final URL.

This CL also adds a test for the blob case, and fixes the test harness
so that the redirect chain behavior is consistent with Chrome (it
previously was not including the final URL in the chain).

(cherry picked from commit 426ce50)

Bug: 1197573
Change-Id: I1e624a31b47fd3f90aec5bb3032f74d19d2b47e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2818720
Commit-Queue: Joe DeBlasio <jdeblasio@chromium.org>
Reviewed-by: Mustafa Emre Acer <meacer@chromium.org>
Reviewed-by: Xing Liu <xingliu@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#871128}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2824021
Auto-Submit: Joe DeBlasio <jdeblasio@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/branch-heads/4472@{#48}
Cr-Branched-From: 3d60439-refs/heads/master@{#870763}

chrome/browser/download/chrome_download_manager_delegate_unittest.cc

@@ -461,6 +461,8 @@ ChromeDownloadManagerDelegateTest::PrepareDownloadItemForMixedContent(
   std::vector<GURL> url_chain;
   if (redirect_url.has_value())
     url_chain.push_back(redirect_url.value());
+  // The redirect chain always contains the final destination at the end.
+  url_chain.push_back(download_url);
   std::unique_ptr<download::MockDownloadItem> download_item =
       CreateActiveDownloadItem(0);
   ON_CALL(*download_item, GetURL())
@@ -507,7 +509,7 @@ void ExpectExtensionOnlyIn(const InsecureDownloadExtensions& ext,
 }
 
 // Determine download target for |download_item| after enabling active content
-// download blocking with the |parameers| enabled. Verify |extension|,
+// download blocking with the |parameters| enabled. Verify |extension|,
 // |interrupt_reason| and |mixed_content_status|. Used by
 // BlockedAsActiveContent_ tests.
 void ChromeDownloadManagerDelegateTest::VerifyMixedContentExtensionOverride(
@@ -931,6 +933,42 @@ TEST_F(ChromeDownloadManagerDelegateTest,
       download::DownloadItem::MixedContentStatus::SAFE);
 }
 
+// Verify that downloads ending in a blob URL are considered secure.
+TEST_F(ChromeDownloadManagerDelegateTest,
+       BlockedAsActiveContent_BlobConsideredSecure) {
+  // Verifies blob URLs are not blocked for active content blocking.
+  const GURL kRedirectUrl("https://example.org/");
+  const GURL kFinalUrl("blob:null/xyz.foo");
+  const auto kSecureOrigin = Origin::Create(GURL("https://example.org"));
+
+  DetermineDownloadTargetResult result;
+  base::test::ScopedFeatureList feature_list;
+  base::HistogramTester histograms;
+
+  std::unique_ptr<download::MockDownloadItem> download_item =
+      PrepareDownloadItemForMixedContent(kFinalUrl, kSecureOrigin,
+                                         kRedirectUrl);
+
+  feature_list.InitAndEnableFeature(features::kTreatUnsafeDownloadsAsActive);
+
+#if BUILDFLAG(ENABLE_PLUGINS)
+  // DownloadTargetDeterminer looks for plugin handlers if there's an
+  // extension.
+  content::PluginService::GetInstance()->Init();
+#endif
+
+  DetermineDownloadTarget(download_item.get(), &result);
+  EXPECT_EQ(download::DOWNLOAD_INTERRUPT_REASON_NONE, result.interrupt_reason);
+  EXPECT_EQ(download::DownloadItem::MixedContentStatus::SAFE,
+            result.mixed_content_status);
+  histograms.ExpectUniqueSample(
+      kInsecureDownloadHistogramName,
+      InsecureDownloadSecurityStatus::kInitiatorSecureFileSecure, 1);
+  ExpectExtensionOnlyIn(InsecureDownloadExtensions::kUnknown,
+                        kInsecureDownloadExtensionInitiatorSecure,
+                        kInsecureDownloadHistogramTargetSecure, histograms);
+}
+
 TEST_F(ChromeDownloadManagerDelegateTest, BlockedAsActiveContent_SilentBlock) {
   // Verifies that active mixed content download silent blocking works by
   // default, and that extensions can be overridden by feature parameter.

chrome/browser/download/mixed_content_download_blocking.cc

@@ -207,10 +207,17 @@ struct MixedContentDownloadData {
 
     // Evaluate download security.
     is_redirect_chain_secure_ = true;
-    for (const auto& url : item->GetUrlChain()) {
-      if (!network::IsUrlPotentiallyTrustworthy(url)) {
-        is_redirect_chain_secure_ = false;
-        break;
+    // Skip over the final URL so that we can investigate it separately below.
+    // The redirect chain always contains the final URL, so this is always safe
+    // in Chrome, but some tests don't plan for it, so we check here.
+    const auto& chain = item->GetUrlChain();
+    if (chain.size() > 1) {
+      for (unsigned i = 0; i < chain.size() - 1; ++i) {
+        const GURL& url = chain[i];
+        if (!network::IsUrlPotentiallyTrustworthy(url)) {
+          is_redirect_chain_secure_ = false;
+          break;
+        }
       }
     }
     const GURL& dl_url = item->GetURL();