Enabled runtime feature BlockingDownloadsInSandbox

LGTMs to ship:
https://groups.google.com/a/chromium.org/g/blink-dev/c/JdAQ6HNoZvk/m/B1aMS33oAAAJ

whatwg/html spec: https://github.com/whatwg/html/pull/4293

Bug: 539938
Change-Id: Ib875fe971ff8ab93ed733f6a0c1d4dd3ee5c7489
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2095602Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Commit-Queue: Yao Xiao <yaoxia@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750209}

chrome/browser/download/download_frame_policy_browsertest.cc

@@ -721,10 +721,7 @@ class DownloadFramePolicyBrowserTest_UpdateIframeSandboxFlags
 
 // Test that when the iframe sandbox attribute is updated before navigation,
 // the updated flag will be controlling the navigation-instantiating frame's
-// policy for the download intervention. Given that the feature is disabled by
-// default, the download will occur, but the point of the test is to track the
-// use counter for whether or not the download would have been blocked by the
-// policy.
+// policy for the download intervention.
 IN_PROC_BROWSER_TEST_P(
     DownloadFramePolicyBrowserTest_UpdateIframeSandboxFlags,
     PendingSandboxPolicyUsedForNavigationInstantiatingFrame) {
@@ -732,6 +729,7 @@ IN_PROC_BROWSER_TEST_P(
   bool from_allow_to_disallow;
   std::tie(is_cross_origin, from_allow_to_disallow) = GetParam();
 
+  size_t number_of_downloads = from_allow_to_disallow ? 0u : 1u;
   SandboxOption initial_sandbox_option =
       from_allow_to_disallow ? SandboxOption::kAllowDownloads
                              : SandboxOption::kDisallowDownloads;
@@ -741,7 +739,7 @@ IN_PROC_BROWSER_TEST_P(
                                     : kSandboxTokensAllowDownloads;
 
   InitializeHistogramTesterAndWebFeatureWaiter();
-  SetNumDownloadsExpectation(1);
+  SetNumDownloadsExpectation(number_of_downloads);
   InitializeOneSubframeSetup(initial_sandbox_option, false /* is_ad_frame */,
                              is_cross_origin);
 
@@ -769,16 +767,14 @@ IN_PROC_BROWSER_TEST_P(
 
 // Test that when the iframe sandbox attribute is updated before navigation,
 // the updated flag will NOT be controlling the navigation-initiator frame's
-// policy for the download intervention. Given that the feature is disabled by
-// default, the download will occur, but the point of the test is to track the
-// use counter for whether or not the download would have been blocked by the
-// policy.
+// policy for the download intervention.
 IN_PROC_BROWSER_TEST_P(DownloadFramePolicyBrowserTest_UpdateIframeSandboxFlags,
                        EffectiveSandboxPolicyUsedForNavigationInitiatorFrame) {
   bool is_cross_origin;
   bool from_allow_to_disallow;
   std::tie(is_cross_origin, from_allow_to_disallow) = GetParam();
 
+  size_t number_of_downloads = from_allow_to_disallow ? 1u : 0u;
   SandboxOption initial_sandbox_option =
       from_allow_to_disallow ? SandboxOption::kAllowDownloads
                              : SandboxOption::kDisallowDownloads;
@@ -788,7 +784,7 @@ IN_PROC_BROWSER_TEST_P(DownloadFramePolicyBrowserTest_UpdateIframeSandboxFlags,
                                     : kSandboxTokensAllowDownloads;
 
   InitializeHistogramTesterAndWebFeatureWaiter();
-  SetNumDownloadsExpectation(1);
+  SetNumDownloadsExpectation(number_of_downloads);
   InitializeOneSubframeSetup(initial_sandbox_option, false /* is_ad_frame */,
                              is_cross_origin);
 

components/page_load_metrics/browser/observers/use_counter_page_load_metrics_observer.cc

@@ -60,10 +60,9 @@ void PossiblyWarnFeatureDeprecation(content::RenderFrameHost* rfh,
     case WebFeature::kDownloadInSandbox:
       rfh->AddMessageToConsole(
           blink::mojom::ConsoleMessageLevel::kWarning,
-          "[Deprecation] Download in sandbox is deprecated and will be removed "
-          "in M81. You may consider adding 'allow-downloads' to the sandbox "
-          "attribute list. See "
-          "https://www.chromestatus.com/feature/5706745674465280 for more "
+          "Download is disallowed. The frame initiating or instantiating the "
+          "download is sandboxed, but the flag ‘allow-downloads’ is not set. "
+          "See https://www.chromestatus.com/feature/5706745674465280 for more "
           "details.");
       return;
     case WebFeature::kDownloadInAdFrameWithoutUserGesture:

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -246,7 +246,7 @@
     },
     {
       name: "BlockingDownloadsInSandbox",
-      status: "test",
+      status: "stable",
     },
     {
       name: "BlockingFocusWithoutUserActivation",