Add half-float vertex attribute caps bit and benchmark

Updates the existing vertex color bench with a half-float mode.
Vanilla GL2/ES2 don't have half-float attributes. The extension
(OES_vertex_half_float) uses a different enum value for the type
parameter. For now, just support GL3/ES3. Otherwise, we could
add a check in GrGLGpu::setupGeometry to re-map GL_HALF_FLOAT
to GL_HALF_FLOAT_OES, based on caps?

Bug: skia:
Change-Id: I1325087db4e615023cceffe1c5b051232769d0ac
Reviewed-on: https://skia-review.googlesource.com/154822
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
6 files changed