Use bytesWritten instead of getOffset on SkDynamicMemoryWStream.

These two methods do the same thing and bytesWritten makes more sense
and is also a proper SkWStream override. As a result, getOffset is being
removed. This updates the calling code.

Test: refactoring CL. Existing unit tests still pass.
Change-Id: I2e2b60c1c86d07c5ab7ec6518d689e8bf700e5d2
1 file changed