[SVG] Update a handful of tests

Several SVG tests were using filters/masks/clips sized in user space
units, but without specifying {filter,mask,clip}Units='userSpaceOnUse'.

Since the default attribute value is 'objectBoundingBox', their size
was incorrectly being resolved against the target bounding box - which
made them susceptible to maximum size capping side effects.

The CL updates these tests to either explicitly specify their units, or
remove the sizing completely when not needed. Also converts some of them
to ref tests.

R=pdr@chromium.org, schenney@chromium.org

Review URL: https://codereview.chromium.org/168593002

git-svn-id: svn://svn.chromium.org/blink/trunk@167247 bbb929c8-8fbe-4397-9dbb-9b2b20218538