Expose environment and arguments to JS

Summary:
Right now from JS there's no way to see the environment variables or arguments that the application was started with.
The main use case for this is to help enable/disable features when being run in a testing environment (as environment variables are the easiest way to communicate).

javache is it okay to reference these constants from JS at startup time? I am planning to disable yellow boxes via an environment variable.

achen1 how easy is it expose these two things for Android as well?

Reviewed By: achen1

Differential Revision: D4395091

fbshipit-source-id: fc318e6a60b8829f7eb4491ea8f3258f68f59c8c

React/Modules/RCTProcessInfo.h

@@ -0,0 +1,15 @@
+/**
+ * Copyright (c) 2017-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 <React/RCTBridge.h>
+#import <React/RCTBridgeModule.h>
+
+@interface RCTProcessInfo : NSObject <RCTBridgeModule>
+
+@end

React/Modules/RCTProcessInfo.m

@@ -0,0 +1,26 @@
+/**
+ * Copyright (c) 2017-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 "RCTProcessInfo.h"
+
+@implementation RCTProcessInfo
+
+RCT_EXPORT_MODULE()
+
+- (NSDictionary *)constantsToExport
+{
+  NSProcessInfo *processInfo = [NSProcessInfo processInfo];
+  return
+  @{
+    @"environment": processInfo.environment,
+    @"arguments": processInfo.arguments,
+    };
+}
+
+@end