Credentials: Remove unnecessary IsSecureContext() check

The CredentialsContainer already declares [SecureContext] extended
attribute at the WebIDL. It makes the interface members exposed to only
secure context in binding level. Therefore, the manual check is
unnecesary because it is always true.

Bug: none
Change-Id: I58afb18a5be83d77d27ff513ef05f2cdaa1bf91a
Reviewed-on: https://chromium-review.googlesource.com/989644Reviewed-by: Balazs Engedy <engedy@chromium.org>
Commit-Queue: Jinho Bang <jinho.bang@samsung.com>
Cr-Commit-Position: refs/heads/master@{#548027}

third_party/WebKit/Source/modules/credentialmanager/CredentialsContainer.cpp

@@ -117,11 +117,8 @@ bool CheckSecurityRequirementsBeforeRequest(
   // execution context is valid, it must have a responsible browsing context.
   SECURITY_CHECK(resolver->GetFrame());
 
-  String error_message;
-  if (!resolver->GetExecutionContext()->IsSecureContext(error_message)) {
-    resolver->Reject(DOMException::Create(kSecurityError, error_message));
-    return false;
-  }
+  // The API is not exposed in non-secure context.
+  SECURITY_CHECK(resolver->GetExecutionContext()->IsSecureContext());
 
   if (required_origin_type == RequiredOriginType::kSecureAndSameWithAncestors &&
       !IsSameOriginWithAncestors(resolver->GetFrame())) {