Auto merge of #15067 - shinglyu:stylo-perf-async, r=Manishearth

Added async performance test

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Add a new way to test arbitrary timing from JavaScript (only for Gecko). This is for Stylo testing.

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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1 files changed, 11 insertions, 1 deletions

diff --git a/etc/ci/performance/gecko_driver.py b/etc/ci/performance/gecko_driver.py
index fe1450d1d1c..8632a1d5f58 100644
--- a/etc/ci/performance/gecko_driver.py
+++ b/etc/ci/performance/gecko_driver.py
@@ -71,7 +71,7 @@ def generate_placeholder(testcase):
         return [timings]
 
 
-def run_gecko_test(testcase, timeout):
+def run_gecko_test(testcase, timeout, is_async):
     with create_gecko_session() as driver:
         driver.set_page_load_timeout(timeout)
         try:
@@ -97,6 +97,16 @@ def run_gecko_test(testcase, timeout):
             print("Failed to get a valid timing measurement.")
             return generate_placeholder(testcase)
 
+        if is_async:
+            # TODO: the timeout is hardcoded
+            driver.implicitly_wait(5)  # sec
+            driver.find_element_by_id("GECKO_TEST_DONE")
+            timings.update(json.loads(
+                driver.execute_script(
+                    "return JSON.stringify(window.customTimers)"
+                )
+            ))
+
     return [timings]