Use Identity matrix for SkTransparentShader.

The SkTransparentShader is just a placeholder that should not
actually be used, so its CTM is not meaningful. However, it needs
to be invertible in order to not assert in SkShader::Context's
constructor. So use SkMatrix::I().

This fixes a CTS test on Android.

R=reed@google.com

Author: scroggo@google.com

Review URL: https://codereview.chromium.org/315743003
1 file changed