Clean up unused code

This sandbox flag was removed, so this is dead code.

Fixed: 1145605
Change-Id: Ibb7fb072f57da918f80644ffc80ae15334b02c0d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2537702
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Commit-Queue: Yu Han <yuzhehan@chromium.org>
Auto-Submit: Mason Freed <masonfreed@chromium.org>
Reviewed-by: Yu Han <yuzhehan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827503}

third_party/blink/renderer/core/html/html_iframe_element_sandbox.cc

@@ -33,10 +33,6 @@ const char* const kSupportedSandboxTokens[] = {
 constexpr char kStorageAccessAPISandboxToken[] =
     "allow-storage-access-by-user-activation";
 
-// TODO(crbug.com/1042130): move this into |kSupportedSandboxTokens| when the
-// feature flag is enabled by default.
-constexpr char kDeclarativeShadowDom[] = "allow-declarative-shadow-dom";
-
 bool IsTokenSupported(const AtomicString& token) {
   for (const char* supported_token : kSupportedSandboxTokens) {
     if (token == supported_token)
@@ -51,14 +47,6 @@ bool IsTokenSupported(const AtomicString& token) {
     return true;
   }
 
-  // If Declarative Shadow DOM is enabled, allow the sandbox flag.
-  // TODO(crbug.com/1145605): This won't work for origin trial enabled iframe
-  // documents, because there's no ExecutionContext here.
-  if (RuntimeEnabledFeatures::DeclarativeShadowDOMEnabledByRuntimeFlag() &&
-      (token == kDeclarativeShadowDom)) {
-    return true;
-  }
-
   return false;
 }