Web: Add sanity check test suite for smaller-footprint builds.

For the smallest builds, google tests will not be present, in
addition to a large number of tests not being capable of running.

Test/web.builtins.vert

@@ -0,0 +1,14 @@
+#version 310 es
+
+layout(location = 0) in mediump float ps;
+
+invariant gl_Position;
+
+void main()
+{
+    gl_Position = vec4(ps);
+    gl_Position *= float(4 - gl_VertexIndex);
+
+    gl_PointSize = ps; 
+    gl_PointSize *= float(5 - gl_InstanceIndex);
+}