Specify dispatchIndirect behavior when exceeding limit (gpuweb#2417)

The rest of the behavior of this command isn't specified yet, but this
gets this into the spec so we can close the issue and edit later.

Fixes gpuweb#323

spec/index.bs

@@ -6856,7 +6856,7 @@ dictionary GPUComputePassDescriptor : GPUObjectDescriptorBase {
                     <div class=validusage>
                         - [$Validate encoder bind groups$](|this|, |this|.{{GPUComputePassEncoder/[[pipeline]]}})
                             is `true`.
-                        - all of |x|, |y| and |z| are less than
+                        - all of |x|, |y| and |z| are less than or equal to
                             |this|.device.limits.{{supported limits/maxComputeWorkgroupsPerDimension}}.
                     </div>
 
@@ -6879,8 +6879,8 @@ dictionary GPUComputePassDescriptor : GPUObjectDescriptorBase {
         See [[#computing-operations]] for the detailed specification.
 
         The <dfn dfn for=>indirect dispatch parameters</dfn> encoded in the buffer must be a tightly
-        packed block of **three 32-bit unsigned integer values (12 bytes total)**, given in the same
-        order as the arguments for {{GPUComputePassEncoder/dispatch()}}. For example:
+        packed block of **three 32-bit unsigned integer values (12 bytes total)**,
+        given in the same order as the arguments for {{GPUComputePassEncoder/dispatch()}}. For example:
 
         <pre highlight="js">
             let dispatchIndirectParameters = new Uint32Array(3);
@@ -6915,7 +6915,9 @@ dictionary GPUComputePassDescriptor : GPUObjectDescriptorBase {
                 1. Add |indirectBuffer| to the [=usage scope=] as {{GPUBufferUsage/INDIRECT}}.
             </div>
 
-            Issue: add some validation related to {{supported limits/maxComputeWorkgroupsPerDimension}}.
+            If any of the dispatch parameters (x, y, or z) is greater than
+            |this|.device.limits.{{supported limits/maxComputeWorkgroupsPerDimension}},
+            no workgroups will be dispatched.
         </div>
 </dl>