This patch disables the initialization of shared memory for d3d backend.
The initialization of shared memory is very slow and may produce
incorrect behavior for some compute shaders on d3d backend.

Bug: angleproject:3226
Change-Id: I41f0f061a5611c52af7667f23938fa48819906b5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1498385Reviewed-by: Jamie Madill (use @chromium please) <jmadill@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jiajia Qin <jiajia.qin@intel.com>