[RPP Observations] Handle prerendered pages correctly

Clicking a link to a prerendered page could trip up the live metrics
model if the frame from the original page is removed before live metrics
handles the interaction event.

This CL skips the step to check if a frame is the primary frame if it
comes from the already known "good" execution context.

Bug: 394918742
Change-Id: I8773d0771690a55a583afaf4ed3d97f4058346ee
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6284568
Reviewed-by: Connor Clark <[email protected]>
Commit-Queue: Adam Raine <[email protected]>

Author: Adam Raine

front_end/models/live-metrics/LiveMetrics.ts

@@ -401,20 +401,25 @@ export class LiveMetrics extends Common.ObjectWrapper.ObjectWrapper<EventTypes>
     // Async tasks can be performed while handling an event (e.g. resolving DOM node)
     // Use a mutex here to ensure the events are handled in the order they are received.
     await this.#mutex.run(async () => {
-      const frame = await this.#getFrameForExecutionContextId(data.executionContextId);
-      if (!frame?.isPrimaryFrame()) {
-        return;
-      }
-
       const webVitalsEvent = JSON.parse(data.payload) as Spec.WebVitalsEvent;
 
-      // Previously injected scripts shouldn't persist, this is just a defensive measure.
-      // Ensure we only handle events from the same execution context as the most recent "reset" event.
-      // "reset" events are only emitted once when the script is injected or a bfcache restoration.
-      if (webVitalsEvent.name === 'reset') {
+      // This ensures that `#lastResetContextId` will always be an execution context on the
+      // primary frame. If we receive events from this execution context then we automatically
+      // know that they are for the primary frame.
+      if (this.#lastResetContextId !== data.executionContextId) {
+        if (webVitalsEvent.name !== 'reset') {
+          return;
+        }
+
+        // We should avoid calling this function for every event.
+        // If an interaction triggers a pre-rendered navigation then the old primary frame could
+        // be removed before we reach this point, and then it will hang forever.
+        const frame = await this.#getFrameForExecutionContextId(data.executionContextId);
+        if (!frame?.isPrimaryFrame()) {
+          return;
+        }
+
         this.#lastResetContextId = data.executionContextId;
-      } else if (this.#lastResetContextId !== data.executionContextId) {
-        return;
       }
 
       await this.#handleWebVitalsEvent(webVitalsEvent, data.executionContextId);