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.h

@@ -0,0 +1,19 @@
+/**
+ * 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 <Foundation/Foundation.h>
+
+#import <React/RCTDefines.h>
+
+@protocol RCTReloadListener
+- (void)didReceiveReloadCommand;
+@end
+
+/** Registers a weakly-held observer of the Command+R reload key command. */
+RCT_EXTERN void RCTRegisterReloadCommandListener(id<RCTReloadListener> listener);