Use SkShader's localMat for SkLocalMatrixShader.

Instead of setting SkShader::fLocalMatrix to Identity and storing
a separate SkMatrix inside SkLocalMatrixShader, reuse
SkShader::fLocalMatrix.

R=reed@google.com

Author: scroggo@google.com

Review URL: https://codereview.chromium.org/386693003
5 files changed