This change can improve the performance of drawElements which uses
the path without translation.
Paste a set of mean data (repeated 30) for reference on Intel skylake
Win10 desktop.
DrawElementsPerfBenchmark.Run/d3d11:
before                     after
mean: 13644.4666667 -> mean: 13887.8333333
DrawElementsPerfBenchmark.Run/d3d11_index_buffer_changed:
before                     after
mean: 45.8          -> mean: 46.3666666667

BUG=755897, angleproject:1393

Change-Id: I11f5db25445346958dfef52b1d23df5483cda32f
Reviewed-on: https://chromium-review.googlesource.com/607413Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>