Bug 1750227 - [devtools] Register cleanup function in initBrowserToolboxTask. r=ochameau.

If a test involving the Browser Toolbox times out, the Browser Toolbox
would not close and could have impact on next tests.
In this patch we register a cleanup function to make sure we always
close the Browser Toolbox.

Differential Revision: https://phabricator.services.mozilla.com/D136096

devtools/client/framework/browser-toolbox/test/helpers-browser-toolbox.js

@@ -172,7 +172,13 @@ async function initBrowserToolboxTask({
     }
   }
 
+  let destroyed = false;
   async function destroy() {
+    // No need to do anything if `destroy` was already called.
+    if (destroyed) {
+      return null;
+    }
+
     const closePromise = process._dbgProcess.wait();
     evaluateExpression("gToolbox.destroy()").catch(e => {
       // Ignore connection close as the toolbox destroy may destroy
@@ -194,8 +200,14 @@ async function initBrowserToolboxTask({
     );
 
     await client.close();
+    destroyed = true;
   }
 
+  // When tests involving using this task fail, the spawned Browser Toolbox is not
+  // destroyed and might impact the next tests (e.g. pausing the content process before
+  // the debugger from the content toolbox does). So make sure to cleanup everything.
+  registerCleanupFunction(destroy);
+
   return {
     importFunctions,
     importScript,