Add a date/details link to FileError deprecation warning

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

Index: third_party/WebKit/Source/core/frame/Deprecation.cpp
diff --git a/third_party/WebKit/Source/core/frame/Deprecation.cpp b/third_party/WebKit/Source/core/frame/Deprecation.cpp
index 424639ea00885eba1c3dca0641b41efd42579fb5..ac708704f08d38c9968e2369474e1386d0a550f7 100644
--- a/third_party/WebKit/Source/core/frame/Deprecation.cpp
+++ b/third_party/WebKit/Source/core/frame/Deprecation.cpp
@@ -180,7 +180,7 @@ String Deprecation::deprecationMessage(UseCounter::Feature feature)
         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).";