After 265569@main, the composite path segments, such as PathDataLine, became decodable by IPC coders only. We need to add StreamConnectionEncoder as additional coder for encoding and decoding them. The reason for this change in 265569@main, was the serialization.in files do not know hot to deal with template struct/class. These composite path segments are defined as templates for two types. So the encoding/decoding code was implemented in WebCoreArgumentCoders.h. This caused a perf regression in MotionMark CanvasLines subtest.