Auto merge of #22714 - aditj:patch-3, r=jdm

Added fetch_start functionality

<!-- Please describe your changes on the following line: -->
Added the fetch_start functionality in http_loader.rs (http_fetch function)

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #21258 (GitHub issue number if applicable)

<!-- Either: -->
- [X] There are tests for these changes OR
- [ ] These changes do not require tests because ___

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/22714)
<!-- Reviewable:end -->

components/net_traits/lib.rs

@@ -447,6 +447,7 @@ pub struct ResourceFetchTiming {
     pub redirect_count: u16,
     pub request_start: u64,
     pub response_start: u64,
+    pub fetch_start: u64,
     // pub response_end: u64,
     // pub redirect_start: u64,
     // pub redirect_end: u64,
@@ -458,6 +459,7 @@ pub enum ResourceAttribute {
     RedirectCount(u16),
     RequestStart,
     ResponseStart,
+    FetchStart,
 }
 
 #[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
@@ -475,6 +477,7 @@ impl ResourceFetchTiming {
             redirect_count: 0,
             request_start: 0,
             response_start: 0,
+            fetch_start: 0,
         }
     }
 
@@ -485,6 +488,7 @@ impl ResourceFetchTiming {
             ResourceAttribute::RedirectCount(count) => self.redirect_count = count,
             ResourceAttribute::RequestStart => self.request_start = precise_time_ns(),
             ResourceAttribute::ResponseStart => self.response_start = precise_time_ns(),
+            ResourceAttribute::FetchStart => self.fetch_start = precise_time_ns(),
         }
     }
 }