When GPUProcess is enabled, a platform path is created in the WebProcess mainly to store the path segments. A path segment is a command added to the Path. When the Path is encoded, the platform path is flattened back to path segments and they are sent to GPUProcess. Upon received the path segments, the GPUProcess creates another platform path to store the decoded path segment.

We should avoid creating the platform path in the WebProcess. For this purpose a new class called PathStream is created. It is a superclass of PathImpl which is the base class of the platform path (PathCG and PathCairo). Path now owns a unique_ptr<PathImpl> which can be converted from PathStream to PathCG and vice versa. Path delegates all the calls to PathImpl. PathStream will implement most of the functions the Path needs. But for drawing and complicated queries, the PathStream will be connoted to PathCG.