Add WebPrescientNetworking to trigger preconnect from Blink.

Source/Platform/Platform.gypi

 #
 # 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:
 #
 #         * 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 94 matching lines @@
             'chromium/public/WebMediaStream.h',
             'chromium/public/WebMediaStreamSource.h',
             'chromium/public/WebMediaStreamSourcesRequest.h',
             'chromium/public/WebMediaStreamTrack.h',
             'chromium/public/WebMessagePortChannel.h',
             'chromium/public/WebMessagePortChannelClient.h',
             'chromium/public/WebMimeRegistry.h',
             'chromium/public/WebNonCopyable.h',
             'chromium/public/WebPluginListBuilder.h',
             'chromium/public/WebPoint.h',
+            'chromium/public/WebPreconnectMotivation.h',
             'chromium/public/WebPrerender.h',
             'chromium/public/WebPrerenderingSupport.h',
             'chromium/public/WebPrivateOwnPtr.h',
             'chromium/public/WebPrivatePtr.h',
             'chromium/public/WebRTCConfiguration.h',
             'chromium/public/WebRTCDTMFSenderHandler.h',
             'chromium/public/WebRTCDTMFSenderHandlerClient.h',
             'chromium/public/WebRTCDataChannelHandler.h',
             'chromium/public/WebRTCDataChannelHandlerClient.h',
             'chromium/public/WebRTCICECandidate.h',
@@ skipping 45 matching lines @@
             'chromium/public/linux/WebFontInfo.h',
             'chromium/public/linux/WebFontRenderStyle.h',
             'chromium/public/linux/WebSandboxSupport.h',
             'chromium/public/mac/WebSandboxSupport.h',
             'chromium/public/mac/WebThemeEngine.h',
             'chromium/public/win/WebSandboxSupport.h',
             'chromium/public/win/WebThemeEngine.h',
         ]
     }
 }