Apply correct sRGB->Linear4f conversion in SkModeColorFilter

This fixes a software rendering bug in Android.  Vector drawable
icons were being drawn "too light" because they were missing this
step.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3563

Change-Id: I9b9c0dc571244dab17ee125ecb7814d7f85181e2
Reviewed-on: https://skia-review.googlesource.com/3563
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
2 files changed