Web: Add compute stage.

Test/web.comp

@@ -0,0 +1,28 @@
+#version 310 es
+
+layout(local_size_x_id = 18, local_size_z_id = 19) in;
+
+layout(local_size_x = 2) in;
+layout(local_size_y = 5) in;
+layout(local_size_z = 7) in;
+const int total = gl_MaxComputeWorkGroupCount.x
+                + gl_MaxComputeWorkGroupCount.y
+                + gl_MaxComputeWorkGroupCount.z
+                + gl_MaxComputeUniformComponents
+                + gl_MaxComputeTextureImageUnits;
+
+shared vec4 s[total];
+
+int arrX[gl_WorkGroupSize.x];
+int arrY[gl_WorkGroupSize.y];
+int arrZ[gl_WorkGroupSize.z];
+
+void main()
+{
+    barrier();
+    memoryBarrier();
+    memoryBarrierShared();
+    groupMemoryBarrier();
+    s[3] = vec4(1.0);
+    s[3] *= arrX[0] * arrY[0] * arrZ[0];
+}