[ReactNative] Fix timers for debugger executors

Summary:
@public

`-[RCTJavaScriptExecutor executeBlockOnJavaScriptQueue:]` would always `dispatch_async`
for the WebView and WebSocket executors, what caused for any frame aligned dispatch.

Test Plan:
Test the `Timers, TimerMixin` example on UIExplorer, `requestAnimationFrame` was
taking ~33.3ms when debugging, now takes ~16.6ms as expected.

Libraries/WebSocket/RCTWebSocketExecutor.m

@@ -185,6 +185,15 @@ RCT_EXPORT_MODULE()
 }
 
 - (void)executeBlockOnJavaScriptQueue:(dispatch_block_t)block
+{
+  if ([NSThread isMainThread]) {
+    block();
+  } else {
+    dispatch_async(dispatch_get_main_queue(), block);
+  }
+}
+
+- (void)executeAsyncBlockOnJavaScriptQueue:(dispatch_block_t)block
 {
   dispatch_async(dispatch_get_main_queue(), block);
 }

React/Executors/RCTWebViewExecutor.m

@@ -182,25 +182,19 @@ RCT_EXPORT_MODULE()
   [_webView loadHTMLString:runScript baseURL:url];
 }
 
-/**
- * In order to avoid `UIWebView` thread locks, all JS executions should be
- * performed outside of the event loop that notifies the `UIWebViewDelegate`
- * that the page has loaded. This is only an issue with the remote debug mode of
- * `UIWebView`. For a production `UIWebView` deployment, this delay is
- * unnecessary and possibly harmful (or helpful?)
- *
- * The delay might not be needed as soon as the following change lands into
- * iOS7. (Review the patch linked here and search for "crash"
- * https://bugs.webkit.org/show_bug.cgi?id=125746).
- */
 - (void)executeBlockOnJavaScriptQueue:(dispatch_block_t)block
 {
-  dispatch_time_t when = dispatch_time(DISPATCH_TIME_NOW, NSEC_PER_MSEC);
 
-  dispatch_after(when, dispatch_get_main_queue(), ^{
-    RCTAssertMainThread();
+  if ([NSThread isMainThread]) {
     block();
-  });
+  } else {
+    dispatch_async(dispatch_get_main_queue(), block);
+  }
+}
+
+- (void)executeAsyncBlockOnJavaScriptQueue:(dispatch_block_t)block
+{
+  dispatch_async(dispatch_get_main_queue(), block);
 }
 
 /**

React/Modules/RCTTiming.m

@@ -182,6 +182,11 @@ RCT_EXPORT_METHOD(createTimer:(NSNumber *)callbackID
   NSTimeInterval jsSchedulingOverhead = -jsSchedulingTime.timeIntervalSinceNow;
   if (jsSchedulingOverhead < 0) {
     RCTLogWarn(@"jsSchedulingOverhead (%ims) should be positive", (int)(jsSchedulingOverhead * 1000));
+
+    /**
+     * Probably debugging on device, set to 0 so we don't ignore the interval
+     */
+    jsSchedulingOverhead = 0;
   }
 
   NSTimeInterval targetTime = jsDuration - jsSchedulingOverhead;