Bug 1727571 - [devtools] Prevent the allocation tracker to record its own modules. r=jdescottes

It was tracking the special sandbox we spawn for builtin-modules.js
as well as its internal sandbox used to fetch platform globals.

Differential Revision: https://phabricator.services.mozilla.com/D124174

devtools/shared/builtin-modules.js

@@ -38,7 +38,7 @@ const {
 
 // Create a single Sandbox to access global properties needed in this module.
 // Sandbox are memory expensive, so we should create as little as possible.
-const debuggerSandbox = Cu.Sandbox(systemPrincipal, {
+const debuggerSandbox = (exports.internalSandbox = Cu.Sandbox(systemPrincipal, {
   // This sandbox is also reused for ChromeDebugger implementation.
   // As we want to load the `Debugger` API for debugging chrome contexts,
   // we have to ensure loading it in a distinct compartment from its debuggee.
@@ -66,7 +66,7 @@ const debuggerSandbox = Cu.Sandbox(systemPrincipal, {
     "URL",
     "XMLHttpRequest",
   ],
-});
+}));
 
 const {
   AbortController,

devtools/shared/test-helpers/allocation-tracker.js

@@ -82,14 +82,28 @@ exports.allocationTracker = function({
     acceptGlobal = () => true;
   } else if (watchDevToolsGlobals) {
     // Only accept globals related to DevTools
+    const builtinGlobal = require("devtools/shared/builtin-modules");
     acceptGlobal = g => {
       // self-hosting-global crashes when trying to call unsafeDereference
       if (g.class == "self-hosting-global") {
+        dump("TRACKER NEW GLOBAL: - : " + g.class + "\n");
         return false;
       }
       const ref = g.unsafeDereference();
       const location = Cu.getRealmLocation(ref);
-      const accept = !!location.match(/devtools/i);
+      let accept = !!location.match(/devtools/i);
+
+      // Also ignore the dedicated Sandbox used to spawn builtin-modules,
+      // as well as its internal Sandbox used to fetch various platform globals.
+      // We ignore the global used by the dedicated loader used to load
+      // the allocation-tracker module.
+      if (
+        ref == Cu.getGlobalForObject(builtinGlobal) ||
+        ref == builtinGlobal.internalSandbox
+      ) {
+        accept = false;
+      }
+
       dump(
         "TRACKER NEW GLOBAL: " + (accept ? "+" : "-") + " : " + location + "\n"
       );