Add WebSerializedOrigin to represent a serialized Web Origin.

Source/platform/blink_platform.gypi

 {
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.cpp',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
       'Clock.h',
       'ColorChooser.cpp',
@@ skipping 277 matching lines @@
       'exported/WebRTCSessionDescriptionRequest.cpp',
       'exported/WebRTCStatsRequest.cpp',
       'exported/WebRTCStatsResponse.cpp',
       'exported/WebRTCVoidRequest.cpp',
       'exported/WebScrollbarImpl.cpp',
       'exported/WebScrollbarImpl.h',
       'exported/WebScrollbarThemeClientImpl.cpp',
       'exported/WebScrollbarThemeClientImpl.h',
       'exported/WebScrollbarThemeGeometryNative.cpp',
       'exported/WebScrollbarThemeGeometryNative.h',
+      'exported/WebSerializedOrigin.cpp',
       'exported/WebServiceWorkerResponse.cpp',
       'exported/WebSocketHandshakeRequestInfo.cpp',
       'exported/WebSocketHandshakeResponseInfo.cpp',
       'exported/WebSocketStreamError.cpp',
       'exported/WebSourceInfo.cpp',
       'exported/WebSpeechSynthesisUtterance.cpp',
       'exported/WebSpeechSynthesisVoice.cpp',
       'exported/WebSpeechSynthesizerClientImpl.cpp',
       'exported/WebSpeechSynthesizerClientImpl.h',
       'exported/WebStorageQuotaCallbacks.cpp',
@@ skipping 609 matching lines @@
       'graphics/Canvas2DLayerManagerTest.cpp',
       'graphics/DeferredImageDecoderTest.cpp',
       'graphics/ImageDecodingStoreTest.cpp',
       'graphics/ImageFrameGeneratorTest.cpp',
       'graphics/gpu/DrawingBufferTest.cpp',
       'graphics/test/MockImageDecoder.h',
       'graphics/test/MockWebGraphicsContext3D.h',
     ],
   },
 }