Add a runtime flag in WebRuntimeFeatures to enable 'image/webp' accept header

Source/WebKit/chromium/public/WebRuntimeFeatures.h

 /*
  * Copyright (C) 2009 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 163 matching lines @@
     WEBKIT_EXPORT static bool isExperimentalContentSecurityPolicyFeaturesEnabled();
 
     WEBKIT_EXPORT static void enableSeamlessIFrames(bool);
     WEBKIT_EXPORT static bool areSeamlessIFramesEnabled();
 
     // If the flag is set, we use WebViewClient::showValidationMessage and
     // hideVlidationMessage for interactive form validation.
     WEBKIT_EXPORT static void enableNativeValidationMessage(bool);
     WEBKIT_EXPORT static bool isNativeValidationMessageEnabled();
 
+    WEBKIT_EXPORT static void enableWebPInAcceptHeader(bool);
+    WEBKIT_EXPORT static bool isWebPInAcceptHeaderEnabled();
+
 private:
     WebRuntimeFeatures();
 };
 
 } // namespace WebKit
 
 #endif