Fix MSVC builds by avoiding a uint to bool warning.
Fix MSVC builds by avoiding a uint to bool warning.

warning C4800: 'const uint8_t' : forcing value to bool 'true' or 'false' (performance warning)

Review URL: http://codereview.appspot.com/79043


csulmone/skia,csulmone/skia,csulmone/skia,csulmone/skia