This a shader compilation error that looks like it might be a bug in Mesa while running top of tree chromium with --enable-unsafe-es3-apis --use-gl=angle on https://www.khronos.org/registry/webgl/sdk/tests/deqp/data/gles3/shaders/scoping.html
You'll find the relevant log below.

Basically a function parameter named S (in int func(int S) below), should shadow the struct S declaration but the error message seems to indicate that it didn't and that it tried to parse a constructor.

The same happens with shadowing from a local variable and shadowing from a local struct declaration.

Note that Mesa (Intel driver) got the translated shader with the mangled names instead.

Please let me know if you need more information.

--original-shader--
#version 300 es
precision mediump float;
bool isOk (int a, int b) { return (a == b); }
layout(location = 0) out mediump vec4 dEQP_FragColor;
in float v_in0;
uniform int ref_out0;
int out0;


struct S { int x; };

int func (int S) { return S; }

void main()
{
	int in0 = int(v_in0 * 1.0025);

	out0 = func(in0);
	bool RES = isOk(out0, ref_out0);
dEQP_FragColor = vec4(RES, RES, RES, 1.0);

}

--translated-shader--
#version 300 es
bool webgl_26daf0ef1d00ab6d(in mediump int webgl_2420662cd003acfa, in mediump int webgl_44a9acbe7629930d){
return (webgl_2420662cd003acfa == webgl_44a9acbe7629930d);
}
layout(location = 0) out mediump vec4 webgl_341844a501096ec4;
in mediump float webgl_c64db3cf02d35b2e;
uniform mediump int webgl_20b06c95b742317e;
mediump int webgl_50c85a6bbb49f119;
struct webgl_bc2ee2bf060ca60{
mediump int webgl_4fc82888d13de398;
} ;
mediump int webgl_8e5fc8b7c9b6652c(in mediump int webgl_bc2ee2bf060ca60){
return webgl_bc2ee2bf060ca60;
}
void main(){
mediump int webgl_e4819ca83edf6f18 = int((webgl_c64db3cf02d35b2e * 1.0025001));
(webgl_50c85a6bbb49f119 = webgl_8e5fc8b7c9b6652c(webgl_e4819ca83edf6f18));
bool webgl_64928d1969e45ae2 = webgl_26daf0ef1d00ab6d(webgl_50c85a6bbb49f119, webgl_20b06c95b742317e);
(webgl_341844a501096ec4 = vec4(webgl_64928d1969e45ae2, webgl_64928d1969e45ae2, webgl_64928d1969e45ae2, 1.0));
}

--info-log--
0:13(29): error: syntax error, unexpected ';', expecting '('