Merge "SkStream: Add SkDynamicMemoryWStream::writeToStream(SkWStream*)" into master-skia

https://skia.googlesource.com/skia/+/7af21501a61886cac94f0bd5e1c14be2dce9ae63

Change-Id: Ie640d4114dd0010d8c9cc2e7a40022a1e2d604cf