Add an assert that we still have a buffer to readFromBuffer().

sk_free(fBuffer.detach()) means fBuffer will be left as NULL, not a zero-length malloc.

BUG=skia:

Review URL: https://codereview.chromium.org/669813002
add gradients and drawPaint to lua

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/667803004
Clean up some warnings about unused code.

BUG=skia:

Review URL: https://codereview.chromium.org/663093004
Rebaseline dftext GM for new color emoji test.

BUG=skia:3033
TBR=mtklein@google.com

Review URL: https://codereview.chromium.org/671513007
Add check to see if we need to remove fixed funciton VA in OptDrawState

BUG=skia:

Review URL: https://codereview.chromium.org/667033003