Move expensive initialization to onOnceBeforeDraw

This was being triggered at viewer startup, while initalizing the slide
list (and then again when switching to the slide). Removing it
declutters startup, particularly if you're trying to debug raster
drawing code.

Bug: skia:
Change-Id: If21cdd10b0dbda74f4a845031ae3e33f7305a1d7
Reviewed-on: https://skia-review.googlesource.com/22742
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed