core: support traces with TracingStartedInBrowser event

lighthouse-core/gather/computed/trace-of-tab.js

@@ -44,19 +44,39 @@ class TraceOfTab extends ComputedArtifact {
     const keyEvents = trace.traceEvents
       .filter(e => {
         return e.cat.includes('blink.user_timing') ||
-          e.cat.includes('loading') ||
-          e.cat.includes('devtools.timeline') ||
-          e.name === 'TracingStartedInPage';
+            e.cat.includes('loading') ||
+            e.cat.includes('devtools.timeline') ||
+            e.cat === '__metadata';
       })
       // @ts-ignore - stableSort added to Array by WebInspector.
       .stableSort((event0, event1) => event0.ts - event1.ts);
 
-    // The first TracingStartedInPage in the trace is definitely our renderer thread of interest
-    // Beware: the tracingStartedInPage event can appear slightly after a navigationStart
-    const startedInPageEvt = keyEvents.find(e => e.name === 'TracingStartedInPage');
+    // Find out the inspected page frame.
+    /** @type {LH.TraceEvent|undefined} */
+    let startedInPageEvt;
+    const startedInBrowserEvt = keyEvents.find(e => e.name === 'TracingStartedInBrowser');
+    if (startedInBrowserEvt && startedInBrowserEvt.args.data &&
+        startedInBrowserEvt.args.data.frames) {
+      const mainFrame = startedInBrowserEvt.args.data.frames.find(frame => !frame.parent);
+      const pid = mainFrame && mainFrame.processId;
+      const threadNameEvt = keyEvents.find(e => e.pid === pid && e.ph === 'M' &&
+        e.cat === '__metadata' && e.name === 'thread_name' && e.args.name === 'CrRendererMain');
+      startedInPageEvt = mainFrame && threadNameEvt ?
+        Object.assign({}, startedInBrowserEvt, {
+          pid, tid: threadNameEvt.tid, name: 'TracingStartedInPage',
+          args: {data: {page: mainFrame.frame}}}) :
+        undefined;
+    }
+    // Support legacy browser versions that do not emit TracingStartedInBrowser event.
+    if (!startedInPageEvt) {
+      // The first TracingStartedInPage in the trace is definitely our renderer thread of interest
+      // Beware: the tracingStartedInPage event can appear slightly after a navigationStart
+      startedInPageEvt = keyEvents.find(e => e.name === 'TracingStartedInPage');
+    }
     if (!startedInPageEvt) throw new LHError(LHError.errors.NO_TRACING_STARTED);
     // @ts-ignore - property chain exists for 'TracingStartedInPage' event.
     const frameId = startedInPageEvt.args.data.page;
+
     // Filter to just events matching the frame ID for sanity
     const frameEvents = keyEvents.filter(e => e.args.frame === frameId);
 
@@ -106,12 +126,12 @@ class TraceOfTab extends ComputedArtifact {
     // stable-sort events to keep them correctly nested.
     /** @type Array<LH.TraceEvent> */
     const processEvents = trace.traceEvents
-      .filter(e => e.pid === startedInPageEvt.pid)
+      .filter(e => e.pid === /** @type {LH.TraceEvent} */ (startedInPageEvt).pid)
       // @ts-ignore - stableSort added to Array by WebInspector.
       .stableSort((event0, event1) => event0.ts - event1.ts);
 
     const mainThreadEvents = processEvents
-      .filter(e => e.tid === startedInPageEvt.tid);
+      .filter(e => e.tid === /** @type {LH.TraceEvent} */ (startedInPageEvt).tid);
 
     const traceEnd = trace.traceEvents.reduce((max, evt) => {
       return max.ts > evt.ts ? max : evt;

lighthouse-core/test/fixtures/traces/threeframes-blank_content_more.json

@@ -20,7 +20,7 @@
 				"tid": 1295,
 				"ts": 900000000000,
 				"ph": "X",
-				"cat": "toplevel",
+				"cat": "devtools.timeline",
 				"name": "TracingStartedInPage",
 				"args": {
 					"data": {

lighthouse-core/test/gather/computed/trace-of-tab-test.js

@@ -112,6 +112,55 @@ describe('Trace of Tab computed artifact:', () => {
     assert.equal(trace.firstMeaningfulPaintEvt, undefined, 'bad fmp');
   });
 
+  it('handles traces with TracingStartedInBrowser events', async () => {
+    const tracingStartedInBrowserTrace = {
+      'traceEvents': [{
+        'pid': 69850,
+        'tid': 69850,
+        'ts': 2193564729582,
+        'ph': 'I',
+        'cat': 'disabled-by-default-devtools.timeline',
+        'name': 'TracingStartedInBrowser',
+        'args': {'data': {
+          'frameTreeNodeId': 1,
+          'frames': [{
+            'frame': 'B192D1F3355A6F961EC8F0B01623C1FB',
+            'url': 'http://www.example.com/',
+            'name': '',
+            'processId': 69920,
+          }],
+        }},
+        'tts': 1085165,
+        's': 't',
+      }, {
+        'pid': 69920,
+        'tid': 1,
+        'ts': 2193564790059,
+        'ph': 'R',
+        'cat': 'blink.user_timing',
+        'name': 'navigationStart',
+        'args': {
+          'frame': 'B192D1F3355A6F961EC8F0B01623C1FB',
+          'data': {
+            'documentLoaderURL': 'http://www.example.com/',
+            'isLoadingMainFrame': true,
+          },
+        },
+        'tts': 141371,
+      }, {
+        'pid': 69920,
+        'tid': 1,
+        'ts': 0,
+        'ph': 'M',
+        'cat': '__metadata',
+        'name': 'thread_name',
+        'args': {'name': 'CrRendererMain'},
+      }]};
+    const trace = await traceOfTab.compute_(tracingStartedInBrowserTrace);
+    assert.equal(trace.startedInPageEvt.ts, 2193564729582);
+    assert.equal(trace.navigationStartEvt.ts, 2193564790059);
+  });
+
   it('stably sorts events', async () => {
     const traceJson = fs.readFileSync(__dirname +
         '/../../fixtures/traces/tracingstarted-after-navstart.json', 'utf8');

typings/externs.d.ts

@@ -137,6 +137,11 @@ declare global {
       cat: string;
       args: {
         data?: {
+          frames?: {
+            frame: string;
+            parent?: string;
+            processId?: number;
+          }[];
           page?: string;
           readyState?: number;
           requestId?: string;
@@ -148,6 +153,7 @@ declare global {
           url?: string;
         };
         frame?: string;
+        name?: string;
       };
       pid: number;
       tid: number;