Before, gradients would only interpolate the linear portion of the
quadratic equation if there was no perspective. This updates them to
do so even in the case that there is perspective. The rearrangement
of math causes noise differences in the following gm tests:
gradients_no_texture_gpu
gradients_view_perspective_gpu
gradients_local_perspective_gpu
gradients_gpu
R=bsalomon@google.com
Author: cdalton@nvidia.com
Review URL: https://codereview.chromium.org/25645006
git-svn-id: http://skia.googlecode.com/svn/trunk@11595 2bbb7eff-a529-9590-31e7-b0007b416f81