BUG=angleproject:197

Changes since first failed patch:
 - Optimized BufferD3D::getStaticVertexBuffer()
 - Removed loop to commit static buffers
 - Out-of-date static buffers (which are much rarer anyway after this patch)
   are marked for deletion at the *next* draw call, rather than searched for
   before each draw call. That search was expensive.

The change should see a net improvement to DrawCallPerfBenchmark for D3D null.

Change-Id: If4942e0afd9e8fefadce8820a1305e13636547ef
Reviewed-on: https://chromium-review.googlesource.com/311115Tested-by: Austin Kinross <aukinros@microsoft.com>
Tryjob-Request: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>