Revert "generate vertex data in onPrepare"

This reverts commit a33a68071b63bbed85e9fadb47dd4ae8da8d519f.

Reason for revert: Old chromebook tool chain

Original change's description:
> generate vertex data in onPrepare
> 
> Switch to a compact encoding for vertex data
> that can be easily expanded in onPrepare.
> 
> Bug: skia:10251
> 
> Change-Id: I53893c94514a7ff3b4f33be444f4ec2002e63ec4
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/290297
> Commit-Queue: Herb Derby <herb@google.com>
> Reviewed-by: Robert Phillips <robertphillips@google.com>
> Reviewed-by: Ben Wagner <bungeman@google.com>

TBR=bungeman@google.com,herb@google.com,robertphillips@google.com

Change-Id: I97d424cfdd1109f2e7c56601e71986926a62c7b1
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:10251
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/291966
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Herb Derby <herb@google.com>
5 files changed