PreloadingDevTools: Add a comment for maybeRegisterNotTriggered

Bug: none
Change-Id: I895868b3bad5a59dbefbdf4f093797bddc6292bd
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/4996793
Auto-Submit: Ken Okada <kenoss@chromium.org>
Reviewed-by: Lingqi Chi <lingqi@chromium.org>
Commit-Queue: Wolfgang Beyer <wolfi@chromium.org>
Reviewed-by: Wolfgang Beyer <wolfi@chromium.org>

front_end/core/sdk/PreloadingModel.ts

diff --git a/front_end/core/sdk/PreloadingModel.ts b/front_end/core/sdk/PreloadingModel.ts
index ef861e6..f35d12e 100644
--- a/front_end/core/sdk/PreloadingModel.ts
+++ b/front_end/core/sdk/PreloadingModel.ts
@@ -534,6 +534,12 @@
     this.map.set(id, attempt);
   }
 
+  // Speculation rules emits a CDP event Preload.preloadingAttemptSourcesUpdated
+  // and an IPC SpeculationHost::UpdateSpeculationCandidates. The latter emits
+  // Preload.prefetch/prerenderAttemptUpdated for each preload attempt triggered.
+  // In general, "Not triggered to triggered" period is short (resp. long) for
+  // eager (resp. non-eager) preloads. For not yet emitted ones, we fill
+  // "Not triggered" preload attempts and show them.
   maybeRegisterNotTriggered(sources: SourceRegistry): void {
     for (const [id, {key}] of sources.entries()) {
       if (this.map.get(id) !== undefined) {