Add Short4 vertex attributes, and benchmark them as 4.12 colors

This reverts commit 90d2d9381e00e223eef1acf7a67ee67c05862b4a.

Updated to use float in the shader (many ES2 implementations
don't support integral types as attributes).

Bug: skia:
Change-Id: I0898f1730da60ff03f8165b2f1a3ee18a7b2fec8
Reviewed-on: https://skia-review.googlesource.com/155162
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
6 files changed