HWUI: mSerialContext needs to outlive other serializing members

mSerialContext is used as the serialization context, and need to
outlive mOpenMultiPicStream and mMultiPic and those are referencing
it in SkSharingSerialContext SkSharingSerialContext::serializeImage

Test: https://buganizer.corp.google.com/issues/182710292#comment16
Bug: 183049238
Change-Id: I25842e492d5efd7a7532964bddca61559d50ebe1