[ReactNative] introduce mountSafeCallback

Summary:
`mountSafeCallback` simply wraps a callback in an `isMounted()` check to prevent crashes when old callbacks are called on unmounted components.

@public

Test Plan:
Added logging and made sure callbacks were getting called through
`mountSafeCallback` and that things worked (e.g. photo viewer rotation etc).

Libraries/ReactIOS/NativeMethodsMixin.js

@@ -20,6 +20,7 @@ var findNodeHandle = require('findNodeHandle');
 var flattenStyle = require('flattenStyle');
 var invariant = require('invariant');
 var mergeFast = require('mergeFast');
+var mountSafeCallback = require('mountSafeCallback');
 var precomputeStyle = require('precomputeStyle');
 
 type MeasureOnSuccessCallback = (
@@ -52,7 +53,11 @@ var animationIDInvariant = function(
 var NativeMethodsMixin = {
   addAnimation: function(anim: number, callback?: (finished: bool) => void) {
     animationIDInvariant('addAnimation', anim);
-    RCTPOPAnimationManager.addAnimation(findNodeHandle(this), anim, callback);
+    RCTPOPAnimationManager.addAnimation(
+      findNodeHandle(this),
+      anim,
+      mountSafeCallback(this, callback)
+    );
   },
 
   removeAnimation: function(anim: number) {
@@ -61,7 +66,10 @@ var NativeMethodsMixin = {
   },
 
   measure: function(callback: MeasureOnSuccessCallback) {
-    RCTUIManager.measure(findNodeHandle(this), callback);
+    RCTUIManager.measure(
+      findNodeHandle(this),
+      mountSafeCallback(this, callback)
+    );
   },
 
   measureLayout: function(
@@ -72,8 +80,8 @@ var NativeMethodsMixin = {
     RCTUIManager.measureLayout(
       findNodeHandle(this),
       relativeToNativeNode,
-      onFail,
-      onSuccess
+      mountSafeCallback(this, onFail),
+      mountSafeCallback(this, onSuccess)
     );
   },
 

Libraries/Utilities/mountSafeCallback.js

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @providesModule mountSafeCallback
+ * @flow
+ */
+'use strict';
+
+var mountSafeCallback = function(context: ReactComponent, callback: ?Function): any {
+  return function() {
+    if (!callback || !context.isMounted()) {
+      return;
+    }
+    return callback.apply(context, arguments);
+  };
+};
+
+module.exports = mountSafeCallback;