Consistently handle startup errors

Summary:
If we use RCTLogError, we show a redbox with a native stacktrace before we can actually show the JS stacktrace (which is only done through dispatch_async). Instead use RCTLogWarn so its logged to console but not reported as a redbox.

Also fix call to RCTNSErrorFromJSErrorRef off the main thread RCTJSCExecutor.

Reviewed By: majak, mmmulani

Differential Revision: D3886813

fbshipit-source-id: 119d04858cb0c85c79e12ff8a79806711f8e0b27

React/Base/RCTBatchedBridge.m

@@ -109,6 +109,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithDelegate:(id<RCTBridgeDelegate>)dele
   __block NSData *sourceCode;
   [self loadSource:^(NSError *error, NSData *source, __unused int64_t sourceLength) {
     if (error) {
+      RCTLogWarn(@"Failed to load source: %@", error);
       dispatch_async(dispatch_get_main_queue(), ^{
         [weakSelf stopLoadingWithError:error];
       });
@@ -153,6 +154,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithDelegate:(id<RCTBridgeDelegate>)dele
       [weakSelf injectJSONConfiguration:config onComplete:^(NSError *error) {
         [performanceLogger markStopForTag:RCTPLNativeModuleInjectConfig];
         if (error) {
+          RCTLogWarn(@"Failed to inject config: %@", error);
           dispatch_async(dispatch_get_main_queue(), ^{
             [weakSelf stopLoadingWithError:error];
           });
@@ -502,7 +504,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithDelegate:(id<RCTBridgeDelegate>)dele
     }
 
     if (loadError) {
-      RCTLogError(@"Failed to execute source code: %@", [loadError localizedDescription]);
+      RCTLogWarn(@"Failed to execute source code: %@", [loadError localizedDescription]);
       dispatch_async(dispatch_get_main_queue(), ^{
         [self stopLoadingWithError:loadError];
       });

React/Executors/RCTJSCExecutor.mm

@@ -828,8 +828,9 @@ static void executeRandomAccessModule(RCTJSCExecutor *executor, uint32_t moduleI
   jscWrapper->JSStringRelease(sourceURL);
 
   if (!result) {
+    NSError *error = RCTNSErrorFromJSErrorRef(jsError, ctx, jscWrapper);
     dispatch_async(dispatch_get_main_queue(), ^{
-      RCTFatal(RCTNSErrorFromJSErrorRef(jsError, ctx, jscWrapper));
+      RCTFatal(error);
       [executor invalidate];
     });
   }