Summary

This commit is being used as proposal for adding a logger (Logger) that allows us to records events happening in the DevTools runtime. In particular, a version of this code was used for collecting profiling data to measure runtime the performance of parseHookNames.

API

The Logger module exposes 2 main functions:

• registerEventLogger: This function allows the caller to register a callback that listens to any log events being emitted from the DevTools runtime.
• logEvent: This function allows the DevTools runtime to log any relevant events. The events that can be logged are statically enforced via Flow, and they can be extended to log different types of events (e.g. other performance or usage metrics).

Both of these functions only work under the new DevTools feature flag: enableLogger, and are no-ops if the flag is not enabled.

As of this commit, the feature flag is completely disabled in every build, and the code being committed is only illustrating how the logger can be used: we are logging an event for measuring the duration for parseHookNames, and we are registering a logger when initializing the DevTools extension. The registered logger is currently a no-op, and in a follow up PR we will add an implementation that actually records those events for internal builds of DevTools only (not open source builds).

Test Plan

• yarn flow
• yarn test
• yarn test-build-devtools
• used this code to collect performance data for parseNamedHooks.
• temporarily enable feature flag and verify events that would be logged: