Bug 1774329 - Add minimal test for GC and CC markers - r=florian

This covers the gc stats' JSONPrinter changes, and would trigger the
verifyJSONStringIsCompact assertion (see next patch) without these changes.

Differential Revision: https://phabricator.services.mozilla.com/D152844

tools/profiler/tests/browser/browser.ini

@@ -18,6 +18,8 @@ support-files = single_frame.html
 
 [browser_test_markers_parent_process.js]
 
+[browser_test_markers_gc_cc.js]
+
 [browser_test_profile_capture_by_pid.js]
 skip-if = os == "win" && os_version == "6.1" # No thread names on win7, needed for these tests
 https_first_disabled = true

tools/profiler/tests/browser/browser_test_markers_gc_cc.js

@@ -0,0 +1,49 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+add_task(async function test_markers_gc_cc() {
+  info("Test GC&CC markers.");
+
+  info("Create a throwaway profile.");
+  await startProfiler({});
+  let tempProfileContainer = { profile: null };
+  tempProfileContainer.profile = await waitSamplingAndStopAndGetProfile();
+
+  info("Restart the profiler.");
+  await startProfiler({});
+
+  info("Throw away the previous profile, which should be garbage-collected.");
+  Assert.equal(
+    typeof tempProfileContainer.profile,
+    "object",
+    "Previously-captured profile should be an object"
+  );
+  delete tempProfileContainer.profile;
+  Assert.equal(
+    typeof tempProfileContainer.profile,
+    "undefined",
+    "Deleted profile should now be undefined"
+  );
+
+  info("Force GC&CC");
+  SpecialPowers.gc();
+  SpecialPowers.forceShrinkingGC();
+  SpecialPowers.forceCC();
+  SpecialPowers.gc();
+  SpecialPowers.forceShrinkingGC();
+  SpecialPowers.forceCC();
+
+  info("Stop the profiler and get the profile.");
+  const profile = await waitSamplingAndStopAndGetProfile();
+
+  const markers = getInflatedMarkerData(profile.threads[0]);
+  Assert.ok(
+    markers.some(({ data }) => data?.type === "GCSlice"),
+    "A GCSlice marker was recorded"
+  );
+  Assert.ok(
+    markers.some(({ data }) => data?.type === "CCSlice"),
+    "A CCSlice marker was recorded"
+  );
+});