Fix KeyNotFoundException on HttpRequestLatencyListener.OnEventWritten for uknown event sources

[ssmelov]

Description

The current implementation of HttpRequestLatencyListener.OnEventWritten always expects that eventSourceName should be available in the _eventToTokenMap dictionary.
Certain events (e.g., EventCounters) bypass the enabled events check, which results in OnEventWritten throwing a KeyNotFoundException.

https://github.com/dotnet/runtime/blob/ac8354e3e94f04fae2d6d942427d025395197f76/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventSource.cs#L2187

Microsoft Reviewers: Open in CodeFlow

Fixes #6822

[Copilot]

Pull Request Overview

This PR fixes a KeyNotFoundException that occurs in HttpRequestLatencyListener.OnEventWritten when handling unknown event sources. The issue arises when events like EventCounters bypass the enabled events check, causing the method to attempt dictionary access with a non-existent key.

• Adds safe dictionary access to prevent KeyNotFoundException when unknown event sources are encountered
• Includes test coverage to verify the fix handles unknown events correctly

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
HttpRequestLatencyListener.cs	Implements safe dictionary access using TryGetValue to prevent KeyNotFoundException
HttpRequestLatencyListenerTest.cs	Adds test to verify unknown events don't cause exceptions or add checkpoints

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[ssmelov]

@dotnet-policy-service agree company="Microsoft"