WebGLRenderTarget: shareDepthFrom in constructor options.

src/renderers/WebGLRenderTarget.js

@@ -29,7 +29,7 @@ THREE.WebGLRenderTarget = function ( width, height, options ) {
 
 	this.generateMipmaps = true;
 
-	this.shareDepthFrom = null;
+	this.shareDepthFrom = options.shareDepthFrom !== undefined ? options.shareDepthFrom : null;
 
 };