This change moves VertexBuffer11::storeVertexAttributes()'s call to
Map() outside a for-loop, eliminating unnecessary calls to Map(). Since
Map() is a relatively expensive operation (even when using NO_OVERWRITE)
this change gives a noticeable performance boost in some scenarios.

Change-Id: I320111b32f2bb9eed92efbd240206e12aaa9964e
Reviewed-on: https://chromium-review.googlesource.com/240181Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Austin Kinross <aukinros@microsoft.com>