Refactor reload command in React Native

Summary: Introduces an API to register a weakly-held listener for the reload (Cmd+R) command. This allows external infrastructure to hook into the reload command before the `RCTBridge` object is even created.

Reviewed By: javache

Differential Revision: D4286980

fbshipit-source-id: 51012fb8cbeb433dc880d9d98d847b07fdbb4c4f

React/Base/RCTReloadCommand.m

@@ -0,0 +1,37 @@
+/**
+ * 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.
+ */
+
+#import "RCTReloadCommand.h"
+
+#import "RCTKeyCommands.h"
+
+void RCTRegisterReloadCommandListener(id<RCTReloadListener> listener)
+{
+  static NSHashTable<id<RCTReloadListener>> *listeners;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    listeners = [NSHashTable weakObjectsHashTable];
+    [[RCTKeyCommands sharedInstance] registerKeyCommandWithInput:@"r"
+                                                   modifierFlags:UIKeyModifierCommand
+                                                          action:
+     ^(__unused UIKeyCommand *command) {
+       NSArray<id<RCTReloadListener>> *copiedListeners;
+       @synchronized (listeners) { // avoid mutation-while-enumerating
+         copiedListeners = [listeners allObjects];
+       }
+       for (id<RCTReloadListener> l in copiedListeners) {
+         [l didReceiveReloadCommand];
+       }
+     }];
+  });
+
+  @synchronized (listeners) {
+    [listeners addObject:listener];
+  }
+}