Gamma correction for distance field text.

Handles both non-LCD and LCD text. Uses a texture to look up the gamma correction values for a given text color or luminance.

BUG=skia:
R=reed@google.com, bungeman@google.com, robertphillips@google.com, bsalomon@google.com

Author: jvanverth@google.com

Review URL: https://codereview.chromium.org/258883002
9 files changed