Update ImGui power sliders in Viewer
Update ImGui power sliders in Viewer

The power sliders have been deprecated in favor of specifying that the
sliders are logarithmic. This doesn't appear to work very well, but at
least it doesn't crash at runtime with an assert.

Change-Id: I2c80aaf8e387efbb878c81a1ca0f754f6c45e80a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/516160
Commit-Queue: Ben Wagner <53965154ffeecc4a10886eab9259e95965f2979a@google.com>
Auto-Submit: Ben Wagner <53965154ffeecc4a10886eab9259e95965f2979a@google.com>
Reviewed-by: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
Commit-Queue: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia