Update chromium.googlesource.com links to use the main branch.

Bug: 842296
Change-Id: Ic6167134552ffa605d638c8ef22272b49621fcfe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3938445
Reviewed-by: Daniel Cheng <[email protected]>
Owners-Override: Daniel Cheng <[email protected]>
Commit-Queue: Daniel Cheng <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1056500}
diff --git a/docs/testing/web_platform_tests_wptrunner.md b/docs/testing/web_platform_tests_wptrunner.md
index 0645edde..57517c16 100644
--- a/docs/testing/web_platform_tests_wptrunner.md
+++ b/docs/testing/web_platform_tests_wptrunner.md
@@ -92,7 +92,7 @@
 Each of these builders has an opt-in trybot mirror with the same name.
 To run one of these builders against a CL, click "Choose Tryjobs" in Gerrit,
 then search for the builder name.
-A [`Cq-Include-Trybots:`](https://chromium.googlesource.com/chromium/src/+/master/docs/contributing.md#cl-footer-reference)
+A [`Cq-Include-Trybots:`](https://chromium.googlesource.com/chromium/src/+/main/docs/contributing.md#cl-footer-reference)
 footer in the CL description can add a `wptrunner` builder to the default CQ
 builder set.
 Results for the bots use the existing layout test