skia: SkPaint::SkPaint(): don't cast away const
skia: SkPaint::SkPaint(): don't cast away const

This will help avoid bugs like the one fixed in change-id:
Iaeb2b84b6696e3eebf29617dfdc41c55e5226776.

Change-Id: I892423e18f9927f827393d0ff0c923259e07389c

UltimatumKang/android_external_skia-1,UltimatumKang/android_external_skia-1,UltimatumKang/android_external_skia-1,UltimatumKang/android_external_skia-1