[WebGPU] GPUComputePassEncoder.dispatch empty call is legal in WebGPU…

…, but generates a validation error in Metal

https://bugs.webkit.org/show_bug.cgi?id=265907
<radar://119217365>

Reviewed by Dan Glastonbury.

Add validation for dispatch and dispatchIndirect which would otherwise
crash the GPU process running the validation CTS test suite.

* Source/WebGPU/WebGPU/ComputePassEncoder.mm:
(WebGPU::ComputePassEncoder::dispatch):
(WebGPU::ComputePassEncoder::dispatchIndirect):

Canonical link: https://commits.webkit.org/271588@main

Source/WebGPU/WebGPU/ComputePassEncoder.mm

@@ -85,13 +85,20 @@
 
 void ComputePassEncoder::dispatch(uint32_t x, uint32_t y, uint32_t z)
 {
+    if (!(x * y * z))
+        return;
+
     executePreDispatchCommands();
     [m_computeCommandEncoder dispatchThreadgroups:MTLSizeMake(x, y, z) threadsPerThreadgroup:m_threadsPerThreadgroup];
 }
 
 void ComputePassEncoder::dispatchIndirect(const Buffer& indirectBuffer, uint64_t indirectOffset)
 {
-    // FIXME: ensure higher levels perform validation on indirectOffset before reaching this callsite
+    if ((indirectOffset % 4) || !(indirectBuffer.usage() & WGPUBufferUsage_Indirect) || (indirectOffset + 3 * sizeof(uint32_t) > indirectBuffer.buffer().length)) {
+        makeInvalid();
+        return;
+    }
+
     executePreDispatchCommands();
     [m_computeCommandEncoder dispatchThreadgroupsWithIndirectBuffer:indirectBuffer.buffer() indirectBufferOffset:indirectOffset threadsPerThreadgroup:m_threadsPerThreadgroup];
 }