[bindings] Implement an ExperimentEnabled IDL extended attribute.

third_party/WebKit/Source/bindings/tests/idls/core/TestInterface.idl

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 18 matching lines @@
  */
 
 // Test for interface extended attributes and special operations.
 // Also used as a target by TestObject
 
 [
     ActiveDOMObject,
     Conditional=CONDITION,
     Custom=LegacyCallAsFunction,
     DoNotCheckConstants,
+    APIExperimentEnabled=ExperimentName,
     ImplementedAs=TestInterfaceImplementation,
     Iterable,
     RuntimeEnabled=FeatureName,
     SetWrapperReferenceTo(TestInterface referencedName),
     Exposed=(Worker,Window),
 ] interface TestInterface : TestInterfaceEmpty {
     // members needed to test [ImplementedAs], as this affect attribute
     // configuration and method configuration
     const unsigned long UNSIGNED_LONG = 0;
     [Reflect=CONST_CPP] const short CONST_JAVASCRIPT = 1;
@@ skipping 68 matching lines @@
     static Promise staticPromiseMethodPartialOverload();
 
     [LenientThis] attribute any lenientThisAttribute;
 
     [LegacyInterfaceTypeChecking] void legacyInterfaceTypeCheckingMethod(TestInterfaceEmpty testInterfaceEmptyArg);
 };
 
 TestInterface implements TestImplements;
 // TestInterface implements TestImplements2; // at implement*ed* interface
 TestInterface implements TestImplements3;