This adds new initializer methods to ASDisplayNode:
```objc
initWithViewBlock:(ASDisplayNodeViewBlock)viewBlock
initWithLayerBlock:(ASDisplayNodeLayerBlock)layerBlock
```
Sometimes a view can't be constructed with `-[initWithViewClass:]` but you want to use it with ASDK, so these new methods provide a way to wrap an existing view in a node.
The API is meant to preserve ASDisplayNode's behavior, so you can still construct and set properties on the node on a background queue before its view is loaded; even though the view was created a priori, it is not considered to be loaded until `node.view` is accessed.
Using the API looks like this:
dispatch_async(backgroundQueue, ^{
ASDisplayNode *node = [ASDisplayNode alloc] initWithViewBlock:^{
// Guaranteed to run on the main queue
UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
[button sizeToFit];
node.frame = button.frame;
return button;
}];
// Use `node` as you normally would...
node.backgroundColor = [UIColor redColor];
});
The main thing this bridging API doesn't do (can't do?) is layout. Methods like `-[ASDisplayNode calculateSizeThatFits:]` and `-[ASDisplayNode layout]` cannot delegate to `[UIView sizeThatFits:]` and `[UIView layoutSubviews]` since the UIView methods must run on the main thread. If ASDK were internally asynchronous and could dispatch its layout methods to different threads (sort of like how ASTableView computes its cells' layouts) then we could mark nodes with externally provided views/layers as having "main-queue affinity" and delegate its layout to UIKit.
Test cases are included and all existing tests pass.
Currently we miss calling `-[super touches*]` on `_ASDisplayView` touch events. We delegate handling to the node which then forwards all touch events to the *superview*, skipping the current view. This seems to have some side effects with `UITableView` and it's cells/content views.
fixes#188
ASRangeController previously enqueued display of individual nodes by
adding their views to the hierarchy, wrapping each `-addSubview:` call
in an explicit CATransaction to force displays to occur in order. This
hack is no longer necessary -- kill it.
