Add feature flag to log JS console messages in system logs

Add flag enable-logging-js-console-messages to allow logging JS console
messages to system logs instead of always logging it.

It's disabled by default because logs may contain PII. It should be
enabled for debugging purposes only.

Bug: 905251
Change-Id: Iee9b3fe2d9256e8fcf1f6e97499d555525f71f48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1528534
Commit-Queue: Hazem Ashmawy <[email protected]>
Reviewed-by: Tobias Sargeant <[email protected]>
Reviewed-by: Jochen Eisinger <[email protected]>
Cr-Commit-Position: refs/heads/master@{#643918}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index af8636ba..26ff541 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -739,6 +739,9 @@
 extern const char kLoadMediaRouterComponentExtensionName[];
 extern const char kLoadMediaRouterComponentExtensionDescription[];
 
+extern const char kLogJsConsoleMessagesName[];
+extern const char kLogJsConsoleMessagesDescription[];
+
 extern const char kLookalikeUrlNavigationSuggestionsName[];
 extern const char kLookalikeUrlNavigationSuggestionsDescription[];