Support missing and invalid defaults for reflected attributes.

Source/bindings/IDLExtendedAttributes.txt

 #
 # This file describes all Blink IDL extended attributes and allowed values.
 # If any IDL file uses an extended attribute or values not listed below, the
 # build will fail.
 # If you would like to add a new extended attribute or value, please:
 #     (1) add the extended attribute or value to this file
 #     (2) add an explanation to the Blink IDL extended attributes document:
 #         http://www.chromium.org/blink/webidl/blink-idl-extended-attributes
 #     (3) add appropriate test cases to run-bindings-tests
 #
@@ skipping 59 matching lines @@
 NotEnumerable
 OverrideBuiltins
 # Valid values for [PerContextEnabled] are Context Features, in
 # ContextFeatures::FeatureType in Source/core/dom/ContextFeatures.h
 PerContextEnabled=*
 PerWorldBindings
 PutForwards=*
 RaisesException=|Getter|Setter|Constructor
 ReadOnly
 Reflect=|*
+ReflectInvalid=*
+ReflectMissing=*
 ReflectOnly=*
 Replaceable
 # Valid values for [RuntimeEnabled] are the Runtime Enabled Features, listed in
 # Source/core/page/RuntimeEnabledFeatures.in
 RuntimeEnabled=*
 SetReference=*
 SetterCallWith=ExecutionContext|ScriptState|ScriptArguments|ActiveWindow|FirstWindow
 SpecialWrapFor=*
 StrictTypeChecking
 TreatNullAs=NullString|*
 TreatReturnedNullStringAs=Null|Undefined
 TreatUndefinedAs=NullString|*
 URL
 Unforgeable