Add MC to check whether canSendEvents_DEPRECATED is needed

Summary:
Changelog: [Internal]

See T118587955

Reviewed By: RSNara

Differential Revision: D36026423

fbshipit-source-id: 26cfcf318af4a5061e94bd0286c0433c06886d8e

Author: p-sun

React/Base/RCTConstants.h

@@ -23,10 +23,10 @@ RCT_EXTERN BOOL RCTGetDispatchW3CPointerEvents(void);
 RCT_EXTERN void RCTSetDispatchW3CPointerEvents(BOOL value);
 
 /*
- * Memory Pressure Unloading
+ * Validate RCTEventEmitter
  */
-RCT_EXTERN BOOL RCTGetDisableBridgeMemoryPressureUnload(void);
-RCT_EXTERN void RCTSetDisableBridgeMemoryPressureUnload(BOOL value);
+RCT_EXTERN BOOL RCTGetValidateCanSendEventInRCTEventEmitter(void);
+RCT_EXTERN void RCTSetValidateCanSendEventInRCTEventEmitter(BOOL value);
 
 /*
  * Memory Pressure Unloading Level

React/Base/RCTConstants.m

@@ -41,18 +41,18 @@ void RCTSetDispatchW3CPointerEvents(BOOL value)
 }
 
 /*
- * Memory Pressure Unloading
+ * Validate RCTEventEmitter. For experimentation only.
  */
-static BOOL RCTDisableBridgeMemoryPressureUnload = NO;
+static BOOL RCTValidateCanSendEventInRCTEventEmitter = NO;
 
-BOOL RCTGetDisableBridgeMemoryPressureUnload()
+BOOL RCTGetValidateCanSendEventInRCTEventEmitter()
 {
-  return RCTDisableBridgeMemoryPressureUnload;
+  return RCTValidateCanSendEventInRCTEventEmitter;
 }
 
-void RCTSetDisableBridgeMemoryPressureUnload(BOOL value)
+void RCTSetValidateCanSendEventInRCTEventEmitter(BOOL value)
 {
-  RCTDisableBridgeMemoryPressureUnload = value;
+  RCTValidateCanSendEventInRCTEventEmitter = value;
 }
 
 /*

React/Modules/RCTEventEmitter.m

@@ -6,6 +6,7 @@
  */
 
 #import "RCTEventEmitter.h"
+#import <React/RCTConstants.h>
 #import "RCTAssert.h"
 #import "RCTLog.h"
 #import "RCTUtils.h"
@@ -83,7 +84,11 @@ - (void)sendEventWithName:(NSString *)eventName body:(id)body
  */
 - (BOOL)canSendEvents_DEPRECATED
 {
-  return _callableJSModules != nil;
+  bool canSendEvents = _callableJSModules != nil;
+  if (!canSendEvents && RCTGetValidateCanSendEventInRCTEventEmitter()) {
+    RCTLogError(@"Trying to send event when _callableJSModules is nil.");
+  }
+  return canSendEvents;
 }
 
 - (void)startObserving