Have sendBeacon throw for Blobs with a type that is not CORS-safelisted.

third_party/WebKit/Source/modules/beacon/NavigatorBeacon.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "modules/beacon/NavigatorBeacon.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/modules/v8/ArrayBufferViewOrBlobOrStringOrFormData.h"
 #include "core/dom/DOMArrayBufferView.h"
 #include "core/dom/ExceptionCode.h"
@@ skipping 108 matching lines @@
         PingLoader::SendBeacon(GetSupplementable()->GetFrame(), allowance, url,
                                data.getAsArrayBufferView().View(), beacon_size);
   } else if (data.isBlob()) {
     Blob* blob = data.getAsBlob();
     if (!FetchUtils::IsSimpleContentType(AtomicString(blob->type()))) {
       UseCounter::Count(context,
                         UseCounter::kSendBeaconWithNonSimpleContentType);
       if (RuntimeEnabledFeatures::
               sendBeaconThrowForBlobWithNonSimpleTypeEnabled()) {
         exception_state.ThrowSecurityError(
-            "sendBeacon() with a Blob whose type is not CORS-safelisted MIME "
-            "type is disallowed experimentally. See http://crbug.com/490015 "
-            "for details.");
+            "sendBeacon() with a Blob whose type is not any of the "
+            "CORS-safelisted values for the Content-Type request header is "
+            "disabled temporarily. See http://crbug.com/490015 for details.");
         return false;
       }
     }
     allowed = PingLoader::SendBeacon(GetSupplementable()->GetFrame(), allowance,
                                      url, blob, beacon_size);
   } else if (data.isString()) {
     allowed = PingLoader::SendBeacon(GetSupplementable()->GetFrame(), allowance,
                                      url, data.getAsString(), beacon_size);
   } else if (data.isFormData()) {
     allowed = PingLoader::SendBeacon(GetSupplementable()->GetFrame(), allowance,
                                      url, data.getAsFormData(), beacon_size);
   } else {
     allowed = PingLoader::SendBeacon(GetSupplementable()->GetFrame(), allowance,
                                      url, String(), beacon_size);
   }
 
   if (!allowed) {
     UseCounter::Count(context, UseCounter::kSendBeaconQuotaExceeded);
     return false;
   }
 
   // Only accumulate transmission size if a limit is imposed.
   if (allowance >= 0)
     AddTransmittedBytes(beacon_size);
   return true;
 }
 
 }  // namespace blink