Add a date/details link to FileError deprecation warning

third_party/WebKit/Source/core/frame/Deprecation.cpp

 // Copyright 2016 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 "core/frame/Deprecation.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/frame/FrameConsole.h"
 #include "core/frame/FrameHost.h"
@@ skipping 162 matching lines @@
 {
     switch (feature) {
     // Quota
     case UseCounter::PrefixedStorageInfo:
         return replacedBy("'window.webkitStorageInfo'", "'navigator.webkitTemporaryStorage' or 'navigator.webkitPersistentStorage'");
 
     case UseCounter::ConsoleMarkTimeline:
         return replacedBy("'console.markTimeline'", "'console.timeStamp'");
 
     case UseCounter::FileError:
-        return "FileError is deprecated. Please use the 'name' or 'message' attributes of DOMError rather than 'code'.";
+        return String::format("'FileError is deprecated and will be removed in %s. Please use the 'name' or 'message' attributes of the error rather than 'code'. See https://www.chromestatus.com/features/6687420359639040 for more details.", milestoneString(54));
 
     case UseCounter::CSSStyleSheetInsertRuleOptionalArg:
         return "Calling CSSStyleSheet.insertRule() with one argument is deprecated. Please pass the index argument as well: insertRule(x, 0).";
 
     case UseCounter::PrefixedVideoSupportsFullscreen:
         return replacedBy("'HTMLVideoElement.webkitSupportsFullscreen'", "'Document.fullscreenEnabled'");
 
     case UseCounter::PrefixedVideoDisplayingFullscreen:
         return replacedBy("'HTMLVideoElement.webkitDisplayingFullscreen'", "'Document.fullscreenElement'");
 
@@ skipping 194 matching lines @@
     case UseCounter::MIDIMessageEventReceivedTime:
         return willBeRemoved("MIDIMessageEvent.receivedTime", 56, "5665772797952000");
 
     // Features that aren't deprecated don't have a deprecation message.
     default:
         return String();
     }
 }
 
 } // namespace blink