core(driver): request smaller trace in m71+

lighthouse-core/gather/driver.js

@@ -916,13 +916,24 @@ class Driver {
   }
 
   /**
-   * @param {{additionalTraceCategories?: string|null}=} settings
+   * @param {LH.Gatherer.PassContext} passContext
    * @return {Promise<void>}
    */
-  beginTrace(settings) {
+  beginTrace(passContext) {
+    const settings = passContext.settings;
     const additionalCategories = (settings && settings.additionalTraceCategories &&
         settings.additionalTraceCategories.split(',')) || [];
     const traceCategories = this._traceCategories.concat(additionalCategories);
+
+    // In Chrome 71+, we trade the chatty 'toplevel' cat for our own, reducing overall trace size
+    // TODO(COMPAT): Once m71 ships to stable, change the traceCategories for real
+    const reChrome71 = /Chrome\/(Headless)?7[1-9]/;
+    if (passContext.hostUserAgent && reChrome71.test(passContext.hostUserAgent)) {
+      traceCategories.forEach((cat, idx) => {
+        if (cat === 'toplevel') traceCategories[idx] = 'disabled-by-default-lighthouse';
+      });
+    }
+
     const uniqueCategories = Array.from(new Set(traceCategories));
 
     // Check any domains that could interfere with or add overhead to the trace.

lighthouse-core/gather/gather-runner.js

@@ -211,11 +211,10 @@ class GatherRunner {
   static async pass(passContext, gathererResults) {
     const driver = passContext.driver;
     const config = passContext.passConfig;
-    const settings = passContext.settings;
     const gatherers = config.gatherers;
-
     const recordTrace = config.recordTrace;
-    const isPerfRun = !settings.disableStorageReset && recordTrace && config.useThrottling;
+    const isPerfRun = !passContext.settings.disableStorageReset && recordTrace &&
+        config.useThrottling;
 
     const gatherernames = gatherers.map(g => g.instance.name).join(', ');
     const status = 'Loading page & waiting for onload';
@@ -226,7 +225,7 @@ class GatherRunner {
     // Always record devtoolsLog
     await driver.beginDevtoolsLog();
     // Begin tracing if requested by config.
-    if (recordTrace) await driver.beginTrace(settings);
+    if (recordTrace) await driver.beginTrace(passContext);
 
     // Navigate.
     await GatherRunner.loadPage(driver, passContext);
@@ -402,6 +401,7 @@ class GatherRunner {
           // If the main document redirects, we'll update this to keep track
           url: options.requestedUrl,
           settings: options.settings,
+          hostUserAgent: baseArtifacts.HostUserAgent,
           passConfig,
           // *pass() functions and gatherers can push to this warnings array.
           LighthouseRunWarnings: baseArtifacts.LighthouseRunWarnings,

lighthouse-core/test/gather/driver-test.js

@@ -224,15 +224,16 @@ describe('Browser Driver', () => {
   });
 
   it('will request default traceCategories', () => {
-    return driverStub.beginTrace().then(() => {
+    return driverStub.beginTrace({settings: {}}).then(() => {
       const traceCmd = sendCommandParams.find(obj => obj.command === 'Tracing.start');
       const categories = traceCmd.params.categories;
       assert.ok(categories.includes('devtools.timeline'), 'contains devtools.timeline');
     });
   });
 
   it('will use requested additionalTraceCategories', () => {
-    return driverStub.beginTrace({additionalTraceCategories: 'v8,v8.execute,toplevel'}).then(() => {
+    const passContext = {settings: {additionalTraceCategories: 'v8,v8.execute,toplevel'}};
+    return driverStub.beginTrace(passContext).then(() => {
       const traceCmd = sendCommandParams.find(obj => obj.command === 'Tracing.start');
       const categories = traceCmd.params.categories;
       assert.ok(categories.includes('blink'), 'contains default categories');
@@ -242,6 +243,18 @@ describe('Browser Driver', () => {
     });
   });
 
+
+  it('will adjust traceCategories based on host user agent', () => {
+    // eslint-disable-next-line max-len
+    const passContext = {hostUserAgent: 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/Headless71.0.3561.0 Safari/537.36'};
+    return driverStub.beginTrace(passContext).then(() => {
+      const traceCmd = sendCommandParams.find(obj => obj.command === 'Tracing.start');
+      const categories = traceCmd.params.categories;
+      assert.ok(categories.includes('disabled-by-default-lighthouse'), 'contains new categories');
+      assert.equal(categories.indexOf('toplevel'), -1, 'excludes toplevel');
+    });
+  });
+
   it('should send the Network.setExtraHTTPHeaders command when there are extra-headers', () => {
     return driverStub.setExtraHTTPHeaders({
       'Cookie': 'monster',

typings/gatherer.d.ts

@@ -18,6 +18,7 @@ declare global {
       passConfig: Config.Pass
       settings: Config.Settings;
       options?: object;
+      hostUserAgent: string;
       /** Push to this array to add top-level warnings to the LHR. */
       LighthouseRunWarnings: Array<string>;
     }