Due to SSBO is translated to RWByteAddressBuffer in HLSL, the corresponding
atomic memory functions atomic* will be translated to
RWByteAddressBuffer.Interlocked*. The translation is like below:

atomicAdd(instanceName.data[0], 5u);
// becomes
uint _ssbo_atomicAdd_uint(RWByteAddressBuffer buffer, uint loc, uint value)
{
    uint original_value;
    buffer.InterlockedAdd(loc, value, original_value);
    return original_value;
}

_ssbo_atomicAdd_uint(_instanceName, 0 + 16 * 0, 5);

Bug: angleproject:1951

Change-Id: If2af8bedb67a4135b443d2512d43c6058a78888d
Reviewed-on: https://chromium-review.googlesource.com/c/1370676Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jiajia Qin <jiajia.qin@intel.com>