[RCTDevLoadingView] Add ability to disable during development.

Summary:
I'd like this ability as this has a tendency to get in the way of some of the more complex UI pieces I have. Disabling RCT_DEV entirely is too much for me.
Closes https://github.com/facebook/react-native/pull/2451
Github Author: Tj <tfallon@mail.depaul.edu>

React/Modules/RCTDevLoadingView.h

@@ -11,4 +11,6 @@
 
 @interface RCTDevLoadingView : NSObject <RCTBridgeModule>
 
++ (void)setEnabled:(BOOL)enabled;
+
 @end

React/Modules/RCTDevLoadingView.m

@@ -16,6 +16,8 @@
 
 #if RCT_DEV
 
+static BOOL isEnabled = YES;
+
 @implementation RCTDevLoadingView
 {
   UIWindow *_window;
@@ -27,6 +29,11 @@
 
 RCT_EXPORT_MODULE()
 
++ (void)setEnabled:(BOOL)enabled
+{
+  isEnabled = enabled;
+}
+
 - (instancetype)init
 {
   if ((self = [super init])) {
@@ -57,6 +64,10 @@ RCT_EXPORT_MODULE()
 
 - (void)showWithURL:(NSURL *)URL
 {
+  if (!isEnabled) {
+    return;
+  }
+
   dispatch_async(dispatch_get_main_queue(), ^{
 
     _showDate = [NSDate date];
@@ -90,6 +101,10 @@ RCT_EXPORT_MODULE()
 
 - (void)hide
 {
+  if (!isEnabled) {
+    return;
+  }
+
   dispatch_async(dispatch_get_main_queue(), ^{
 
     const NSTimeInterval MIN_PRESENTED_TIME = 0.6;
@@ -117,6 +132,7 @@ RCT_EXPORT_MODULE()
 @implementation RCTDevLoadingView
 
 + (NSString *)moduleName { return nil; }
++ (void)setEnabled:(BOOL)enabled { }
 
 @end