core(audits): prevent yield-bounded tasks from being reported as long tasks

The original issue reported that both Total Blocking Time (TBT) and
JavaScript execution time were being artificially inflated during
simulated mobile throttling.

While the Total CPU Time math is technically correct across the whole page,
the simulated long tasks were appearing in the `long-tasks` audit table.
This commit ensures the `long-tasks` audit respects the original
unthrottled duration of tasks bounded by `scheduler.yield` or
`scheduler.postTask`, preventing them from falsely polluting the list
of input delay contributors.

Fixes #16183

Author: connorjclark

cli/test/smokehouse/test-definitions/lantern-scheduler-apis.js

@@ -24,6 +24,13 @@ const expectations = [
         'total-blocking-time': {
           numericValue: '<=100',
         },
+        'long-tasks': {
+          details: {
+            items: {
+              length: 0,
+            },
+          },
+        },
       },
     },
   },
@@ -35,6 +42,13 @@ const expectations = [
         'total-blocking-time': {
           numericValue: '<=100',
         },
+        'long-tasks': {
+          details: {
+            items: {
+              length: 0,
+            },
+          },
+        },
       },
     },
   },

core/audits/long-tasks.js

@@ -199,7 +199,21 @@ class LongTasks extends Audit {
       const simulation = simulator.simulate(pageGraph, {label: 'long-tasks-diagnostic'});
       for (const [node, timing] of simulation.nodeTimings.entries()) {
         if (node.type !== 'cpu') continue;
-        taskTimingsByEvent.set(node.event, timing);
+
+        let duration = timing.duration;
+        // @ts-expect-error - childEvents is not typed
+        const isYieldBounded = node.childEvents?.some(e => {
+          return e.name === 'ScheduleYieldContinuation' ||
+                 e.name === 'RunYieldContinuation' ||
+                 e.name === 'SchedulePostTaskCallback' ||
+                 e.name === 'RunPostTaskCallback';
+        });
+
+        if (isYieldBounded) {
+          duration = node.duration / 1000;
+        }
+
+        taskTimingsByEvent.set(node.event, {...timing, duration});
       }
     }