[wptrunner] Collect per-test trace events from Chromium

When `wpt run --trace-categories` is specified, the trace events [0] are
retrieved from an internal ChromeDriver buffer and logged as an `extra`
test result field. The trace will be consumed by an event listener on
the Chromium side (https://crrev.com/c/6820247) and can be viewed in
https://ui.perfetto.dev/.

Partially fulfills crbug.com/434017035

[0]: https://developer.chrome.com/docs/chromedriver/logging/performance-log

Author: jonathan-j-lee

tools/wptrunner/wptrunner/browsers/chrome.py

@@ -86,6 +86,15 @@ def executor_kwargs(logger, test_type, test_environment, run_info_data, subsuite
         # fail to create a session if they don't recognize this capability.
         chrome_options["quitGracefully"] = True
 
+    if trace_categories := kwargs.get("trace_categories"):
+        executor_kwargs["enable_tracing"] = True
+        capabilities["goog:loggingPrefs"] = {
+            "performance": "INFO",
+        }
+        chrome_options["perfLoggingPrefs"] = {
+            "traceCategories": trace_categories,
+        }
+
     # Here we set a few Chrome flags that are always passed.
     # ChromeDriver's "acceptInsecureCerts" capability only controls the current
     # browsing context, whereas the CLI flag works for workers, too.

tools/wptrunner/wptrunner/executors/executorchrome.py

@@ -185,13 +185,46 @@ def execute_cdp_command(self, command, params=None):
                                                    body=body)
 
 
+class ChromeDriverTracingProtocolPart(ProtocolPart):
+    name = "tracing"
+
+    def setup(self):
+        self.webdriver = self.parent.webdriver
+
+    def get_trace(self):
+        """Retrieve trace events accumulated by ChromeDriver.
+
+        This also clears ChromeDriver's internal buffer of logged events.
+
+        Returns:
+            JSON in the trace array format [0].
+
+        [0]: https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview?tab=t.0#heading=h.f2f0yd51wi15
+        """
+        # Not a standard WebDriver method.
+        perf_data = self.webdriver.send_session_command("POST", "se/log", {
+            "type": "performance",
+        })
+        events = []
+        for entry in perf_data:
+            # Unwrap the inner trace event and discard the unnecessary
+            # ChromeDriver-added fields.
+            data_collected_event = json.loads(entry["message"]).get("message", {})
+            if data_collected_event.get("method") != "Tracing.dataCollected":
+                continue
+            if trace_event := data_collected_event.get("params"):
+                events.append(trace_event)
+        return events
+
+
 class ChromeDriverProtocol(WebDriverProtocol):
     implements = [
         ChromeDriverBaseProtocolPart,
         ChromeDriverDevToolsProtocolPart,
         ChromeDriverFedCMProtocolPart,
         ChromeDriverTestDriverProtocolPart,
         ChromeDriverTestharnessProtocolPart,
+        ChromeDriverTracingProtocolPart,
     ]
     for base_part in WebDriverProtocol.implements:
         if base_part.name not in {part.name for part in implements}:
@@ -258,24 +291,39 @@ def convert_result(self, test, result, **kwargs):
 class ChromeDriverCrashTestExecutor(WebDriverCrashtestExecutor):
     protocol_cls = ChromeDriverProtocol
 
-    def __init__(self, *args, sanitizer_enabled=False, **kwargs):
+    def __init__(self, *args, sanitizer_enabled=False, enable_tracing=False, **kwargs):
         super().__init__(*args, **kwargs)
         self.sanitizer_enabled = sanitizer_enabled
+        self.enable_tracing = enable_tracing
+
+    def do_test(self, test):
+        file_result, subtest_results = super().do_test(test)
+        if self.enable_tracing:
+            file_result.extra["trace"] = self.protocol.tracing.get_trace()
+        return file_result, subtest_results
 
 
 @_evaluate_sanitized_result
 class ChromeDriverRefTestExecutor(WebDriverRefTestExecutor):
     protocol_cls = ChromeDriverProtocol
 
-    def __init__(self, *args, sanitizer_enabled=False, **kwargs):
+    def __init__(self, *args, sanitizer_enabled=False, enable_tracing=False, **kwargs):
         super().__init__(*args, **kwargs)
         self.sanitizer_enabled = sanitizer_enabled
+        self.enable_tracing = enable_tracing
+
+    def do_test(self, test):
+        file_result, subtest_results = super().do_test(test)
+        if self.enable_tracing:
+            file_result.extra["trace"] = self.protocol.tracing.get_trace()
+        return file_result, subtest_results
 
 
 @_evaluate_sanitized_result
 class ChromeDriverTestharnessExecutor(WebDriverTestharnessExecutor):
 
-    def __init__(self, *args, sanitizer_enabled=False, reuse_window=False, **kwargs):
+    def __init__(self, *args, sanitizer_enabled=False, enable_tracing=False, reuse_window=False,
+                 **kwargs):
         require_webdriver_bidi = kwargs.get("browser_settings", {}).get(
             "require_webdriver_bidi", None)
         if require_webdriver_bidi:
@@ -285,6 +333,7 @@ def __init__(self, *args, sanitizer_enabled=False, reuse_window=False, **kwargs)
 
         super().__init__(*args, **kwargs)
         self.sanitizer_enabled = sanitizer_enabled
+        self.enable_tracing = enable_tracing
         self.reuse_window = reuse_window
 
     def create_test_window(self, protocol):
@@ -312,11 +361,24 @@ def create_test_window(self, protocol):
             self.protocol.testharness.persistent_test_window = test_window
         return test_window
 
+    def do_test(self, test):
+        file_result, subtest_results = super().do_test(test)
+        if self.enable_tracing:
+            file_result.extra["trace"] = self.protocol.tracing.get_trace()
+        return file_result, subtest_results
+
 
 @_evaluate_sanitized_result
 class ChromeDriverPrintRefTestExecutor(WebDriverPrintRefTestExecutor):
     protocol_cls = ChromeDriverProtocol
 
-    def __init__(self, *args, sanitizer_enabled=False, **kwargs):
+    def __init__(self, *args, sanitizer_enabled=False, enable_tracing=False, **kwargs):
         super().__init__(*args, **kwargs)
         self.sanitizer_enabled = sanitizer_enabled
+        self.enable_tracing = enable_tracing
+
+    def do_test(self, test):
+        file_result, subtest_results = super().do_test(test)
+        if self.enable_tracing:
+            file_result.extra["trace"] = self.protocol.tracing.get_trace()
+        return file_result, subtest_results

tools/wptrunner/wptrunner/wptcommandline.py

@@ -381,6 +381,12 @@ def create_parser(product_choices=None):
         help=("Reuse a window across `testharness.js` tests where possible, "
               "which can speed up testing. Also useful for ensuring that the "
               "renderer process has a stable PID for a debugger to attach to."))
+    chrome_group.add_argument(
+        "--trace-categories",
+        metavar="CATEGORIES",
+        nargs="?",
+        const="blink,blink.bindings",
+        help="Record traces under the given categories for each test.")
 
     sauce_group = parser.add_argument_group("Sauce Labs-specific")
     sauce_group.add_argument("--sauce-browser", help="Sauce Labs browser name")