Stop counting kWorkerAllowedByChildBlockedByScript

To reduce GetDocument() usage.
As https://github.com/w3c/webappsec-csp/issues/146 has already been
closed and the Blink implemetation has been changed,
this UseCounter is no longer needed.

Bug: 878274
Change-Id: Icb55058d369b29992436229a9b971bc6f0b8f2a6
Reviewed-on: https://chromium-review.googlesource.com/c/1192303Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614762}

third_party/blink/public/platform/web_feature.mojom

@@ -155,8 +155,6 @@ enum WebFeature {
   kFormAssociationByParser = 248,
   kSVGSVGElementInDocument = 250,
   kSVGDocumentRootElement = 251,
-  kWorkerSubjectToCSP = 257,
-  kWorkerAllowedByChildBlockedByScript = 258,
   kDeprecatedWebKitGradient = 260,
   kDeprecatedWebKitLinearGradient = 261,
   kDeprecatedWebKitRepeatingLinearGradient = 262,

third_party/blink/renderer/core/frame/csp/content_security_policy.cc

@@ -1038,41 +1038,6 @@ bool ContentSecurityPolicy::AllowWorkerContextFromSource(
     RedirectStatus redirect_status,
     SecurityViolationReportingPolicy reporting_policy,
     CheckHeaderType check_header_type) const {
-  // CSP 1.1 moves workers from 'script-src' to the new 'child-src'. Measure the
-  // impact of this backwards-incompatible change.
-  // TODO(mkwst): We reverted this.
-  if (Document* document = this->GetDocument()) {
-    UseCounter::Count(*document, WebFeature::kWorkerSubjectToCSP);
-    bool is_allowed_worker = true;
-    if (!ShouldBypassContentSecurityPolicy(url, execution_context_)) {
-      for (const auto& policy : policies_) {
-        if (!CheckHeaderTypeMatches(check_header_type, policy->HeaderType()))
-          continue;
-        is_allowed_worker &= policy->AllowWorkerFromSource(
-            url, redirect_status,
-            SecurityViolationReportingPolicy::kSuppressReporting);
-      }
-    }
-
-    bool is_allowed_script = true;
-
-    if (!ShouldBypassContentSecurityPolicy(url, execution_context_)) {
-      for (const auto& policy : policies_) {
-        if (!CheckHeaderTypeMatches(check_header_type, policy->HeaderType()))
-          continue;
-        is_allowed_script &= policy->AllowScriptFromSource(
-            url, AtomicString(), IntegrityMetadataSet(), kNotParserInserted,
-            redirect_status,
-            SecurityViolationReportingPolicy::kSuppressReporting);
-      }
-    }
-
-    if (is_allowed_worker && !is_allowed_script) {
-      UseCounter::Count(*document,
-                        WebFeature::kWorkerAllowedByChildBlockedByScript);
-    }
-  }
-
   if (ShouldBypassContentSecurityPolicy(url, execution_context_))
     return true;