Disable actions when writing to CALayer properties.

Summary: We don't want CALayer writes to create implicit animations.

Reviewers: O2 Material Motion, O4 Material Apple platform reviewers, #material_motion, chuga

Reviewed By: O4 Material Apple platform reviewers, chuga

Tags: #material_motion

Differential Revision: http://codereview.cc/D2797

src/reactivetypes/ReactiveCALayer.swift

@@ -115,7 +115,12 @@ public class ReactiveCALayer {
   fileprivate func property<T>(_ name: String, initialValue: T, externalWrite: @escaping NextChannel<T>, keyPath: String) -> ReactiveProperty<T> {
     let layer = self.layer
     var lastAnimationKey: String?
-    let property = ReactiveProperty(name, initialValue: initialValue, externalWrite: externalWrite, coreAnimation: { [weak self] event in
+    let property = ReactiveProperty(name, initialValue: initialValue, externalWrite: { value in
+      let actionsWereDisabled = CATransaction.disableActions()
+      CATransaction.setDisableActions(false)
+      externalWrite(value)
+      CATransaction.setDisableActions(actionsWereDisabled)
+    }, coreAnimation: { [weak self] event in
       guard let strongSelf = self else { return }
       switch event {
       case .add(let animation, let key, let initialVelocity, let completionBlock):