Remove CSS_REGIONS compile flag from Blink.

Source/core/page/DOMWindow.idl

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2011 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 509 matching lines @@
     attribute StorageEventConstructor StorageEvent;
     [Conditional=INPUT_SPEECH] attribute SpeechInputEventConstructor SpeechInputEvent;
     [Conditional=WEBGL] attribute WebGLContextEventConstructor WebGLContextEvent;
     [EnabledAtRuntime=requestAutocomplete] attribute AutocompleteErrorEventConstructor AutocompleteErrorEvent;
     [EnabledAtRuntime=experimentalContentSecurityPolicyFeatures] attribute SecurityPolicyViolationEventConstructor SecurityPolicyViolationEvent;
 
     attribute EventExceptionConstructor EventException;
 
     attribute WebKitCSSKeyframeRuleConstructor WebKitCSSKeyframeRule;
     attribute WebKitCSSKeyframesRuleConstructor WebKitCSSKeyframesRule;
-    [Conditional=CSS_REGIONS, EnabledAtRuntime=cssRegions] attribute WebKitCSSRegionRuleConstructor WebKitCSSRegionRule;
+    [EnabledAtRuntime=cssRegions] attribute WebKitCSSRegionRuleConstructor WebKitCSSRegionRule;
 
     attribute WebKitCSSMatrixConstructor WebKitCSSMatrix; // Usable with the new operator
 
     attribute DOMPointConstructor WebKitPoint; // Usable with new the operator
 
     attribute ClipboardConstructor Clipboard;
 
     attribute WorkerConstructor Worker; // Usable with the new operator
     [EnabledAtRuntime] attribute SharedWorkerConstructor SharedWorker; // Usable with the new operator
 
@@ skipping 205 matching lines @@
     attribute MutationRecordConstructor MutationRecord;
 
     [EnabledAtRuntime=mediaSource] attribute MediaSourceConstructor WebKitMediaSource;
     [EnabledAtRuntime=mediaSource] attribute SourceBufferConstructor WebKitSourceBuffer;
     [EnabledAtRuntime=mediaSource] attribute SourceBufferListConstructor WebKitSourceBufferList;
 
     // window.toString() requires special handling in V8
     [DoNotCheckSignature, DoNotCheckSecurity, Custom, NotEnumerable] DOMString toString();
 };