3/n Easy: Add MC to gate parsing unhandled JS errors in C++

Summary:
Changelog:
[Internal][ErrorHandling] 3/n Add a gate for parsing unhandled JS errors in C++

Gate this just in case it causes issues. Enabling this is definitely a better behavior than before, because we want the JS stack when there is a JS error, not the native stack.

Reviewed By: sammy-SC

Differential Revision: D40397393

fbshipit-source-id: 586b4d7bcf710edb048b5c643646ba2f3c4c302a

React/Base/RCTConstants.h

@@ -75,3 +75,9 @@ RCT_EXTERN void RCTSetValidateCanSendEventInRCTEventEmitter(BOOL value);
  */
 RCT_EXTERN BOOL RCTGetMemoryPressureUnloadLevel(void);
 RCT_EXTERN void RCTSetMemoryPressureUnloadLevel(int value);
+
+/*
+ * Parse JS stack for unhandled JS errors caught in C++
+ */
+RCT_EXTERN BOOL RCTGetParseUnhandledJSErrorStackNatively(void);
+RCT_EXTERN void RCTSetParseUnhandledJSErrorStackNatively(BOOL value);

React/Base/RCTConstants.m

@@ -65,3 +65,19 @@ void RCTSetMemoryPressureUnloadLevel(int value)
 {
   RCTMemoryPressureUnloadLevel = value;
 }
+
+/*
+ * In Bridge mode, parse the JS stack for unhandled JS errors, to display in RedBox.
+ * When false (previous default behavior), a native stack is displayed in the RedBox.
+ */
+static BOOL RCTParseUnhandledJSErrorStackNatively = NO;
+
+BOOL RCTGetParseUnhandledJSErrorStackNatively()
+{
+  return RCTParseUnhandledJSErrorStackNatively;
+}
+
+void RCTSetParseUnhandledJSErrorStackNatively(BOOL value)
+{
+  RCTParseUnhandledJSErrorStackNatively = value;
+}