Update TestScalarMaterialMode test image size.

Since certain dashboards have issues with large windows, we reduce this
test's window size. This should address such issues.

Change-Id: Ibf4edd9291fb45834d3c944cd5b395653b183a5e
Merge topic 'fix_scalar_material_mode_test' into master

a765c1ad Update TestScalarMaterialMode test image size.