Bug 1611817 - Fix race condition in DevTools shutdown and stopProfilerAndDiscardProfile; r=julienw

This race condition is really only exposed in automated testing, but it
was making the DevTools performance-new mochitests intermittent.

The race looks like this:

* stopProfilerAndDiscardProfiler() request
* perf actor process the request
* The gecko profiler sends an event notifying that the profiler stopped
* DevTools updates the UI upon receiving the event
* The test suite sees the UI update, and triggers a close of DevTools
* Error: Connection closed, pending request
* stopProfilerAndDiscardProfiler still hasn't sent the response yet

This patch fixes it by not throwing an error if the panel is already destroyed.

Differential Revision: https://phabricator.services.mozilla.com/D65150

--HG--
extra : moz-landing-system : lando

devtools/client/performance-new/@types/perf.d.ts

@@ -15,7 +15,8 @@ export interface PanelWindow {
   gToolbox?: any;
   gInit(perfFront: PerfFront, preferenceFront: PageContext): void;
   gDestroy(): void;
-  gReportReady?(): void
+  gReportReady?(): void;
+  gIsPanelDestroyed?: boolean;
 }
 
 /**

devtools/client/performance-new/panel.js

@@ -56,6 +56,7 @@ class PerformancePanel {
    */
   async _doOpen() {
     this.panelWin.gToolbox = this.toolbox;
+    this.panelWin.gIsPanelDestroyed = false;
 
     const perfFront = await this.target.client.mainRoot.getFront("perf");
 
@@ -82,6 +83,7 @@ class PerformancePanel {
     this.panelWin.gDestroy();
     this.emit("destroyed");
     this._destroyed = true;
+    this.panelWin.gIsPanelDestroyed = true;
   }
 }
 

devtools/client/performance-new/store/actions.js

@@ -21,6 +21,7 @@ const {
  * @typedef {import("../@types/perf").RecordingState} RecordingState
  * @typedef {import("../@types/perf").InitializeStoreValues} InitializeStoreValues
  * @typedef {import("../@types/perf").Presets} Presets
+ * @typedef {import("../@types/perf").PanelWindow} PanelWindow
  */
 
 /**
@@ -230,6 +231,22 @@ exports.stopProfilerAndDiscardProfile = () => {
   return async (dispatch, getState) => {
     const perfFront = selectors.getPerfFront(getState());
     dispatch(changeRecordingState("request-to-stop-profiler"));
-    perfFront.stopProfilerAndDiscardProfile();
+
+    try {
+      await perfFront.stopProfilerAndDiscardProfile();
+    } catch (error) {
+      /** @type {any} */
+      const anyWindow = window;
+      /** @type {PanelWindow} - Coerce the window into the PanelWindow. */
+      const { gIsPanelDestroyed } = anyWindow;
+
+      if (gIsPanelDestroyed) {
+        // This error is most likely "Connection closed, pending request" as the
+        // command can race with closing the panel. Do not report an error. It's
+        // most likely fine.
+      } else {
+        throw error;
+      }
+    }
   };
 };