WebGLProgram: Fixed gsls warning.

src/renderers/shaders/ShaderChunk/logdepthbuf_pars_fragment.glsl

@@ -4,9 +4,8 @@
 
 	#ifdef USE_LOGDEPTHBUF_EXT
 
-		#extension GL_EXT_frag_depth : enable
 		varying float vFragDepth;
 
 	#endif
 
-#endif
+#endif

src/renderers/webgl/WebGLProgram.js

@@ -281,6 +281,7 @@ THREE.WebGLProgram = ( function () {
 			prefixFragment = [
 
 				( parameters.bumpMap || parameters.normalMap || parameters.flatShading || material.derivatives ) ? '#extension GL_OES_standard_derivatives : enable' : '',
+				parameters.logarithmicDepthBuffer && renderer.extensions.get( 'EXT_frag_depth' ) ? '#extension GL_EXT_frag_depth : enable' : '',
 
 				'precision ' + parameters.precision + ' float;',
 				'precision ' + parameters.precision + ' int;',