Selective refresh very slow or fails when JS Widgets active on 4.7-RC1

[westonruter]

For some reason when the JS Widgets plugin is active, selective refresh of post fields is 5x slower.

1. Active JS Widgets.
2. Make a change to a post title.
3. Notice that it response slowly compared when JS Widgets it not active.

Short circuiting WP_Customize_Post_Field_Partial::render_callback() causes the slowness to go away, but naturally none of the code runs. Seems like a problem in setup_postdata() or in the filters that apply in WP_Customize_Post_Field_Partial::render_post_title().

[westonruter]

With the JS Widgets plugin activated, hooks that take longer than 0.1s accumulatively:

tag: the_title
	duration sum: 0.746872s
	count: 61
tag: wp_insert_post_data
	duration sum: 2.182451s
	count: 14
tag: the_post
	duration sum: 1.321027s
	count: 4

And with the JS Widgets plugin deactivated, hooks that take longer than 0.1s accumulatively:

tag: wp_insert_post_data
	duration sum: 0.218897
	count: 14
tag: the_post
	duration sum: 0.117028
	count: 4

Count is the number of callbacks that get invoked.

[westonruter]

It turns out to be an issue with Stream. PR opened to fix in that plugin: xwp/stream#898