Unify setting postprocessing pass size

The size is now set the same way in EffectComposer.addPass() and EffectComposer.setSize().

examples/jsm/postprocessing/EffectComposer.js

@@ -90,9 +90,7 @@ Object.assign( EffectComposer.prototype, {
 	addPass: function ( pass ) {
 
 		this.passes.push( pass );
-
-		var size = this.renderer.getDrawingBufferSize( new Vector2() );
-		pass.setSize( size.width, size.height );
+		pass.setSize( this._width * this._pixelRatio, this._height * this._pixelRatio );
 
 	},