Update threshold to 50ms and update tests.

Author: tejasd

firebase-perf/src/main/java/com/google/firebase/perf/metrics/AppStartTrace.java

@@ -77,7 +77,7 @@ public class AppStartTrace implements ActivityLifecycleCallbacks, LifecycleObser
 
   // If the `mainThreadRunnableTime` was set within this duration, the assumption
   // is that it was called immediately before `onActivityCreated` in foreground starts on API 34+.
-  private static final long MAX_BACKGROUND_RUNNABLE_DELAY = TimeUnit.MILLISECONDS.toMicros(100);
+  private static final long MAX_BACKGROUND_RUNNABLE_DELAY = TimeUnit.MILLISECONDS.toMicros(50);
 
   // Core pool size 0 allows threads to shut down if they're idle
   private static final int CORE_POOL_SIZE = 0;

firebase-perf/src/test/java/com/google/firebase/perf/metrics/AppStartTraceTest.java

@@ -239,15 +239,16 @@ public void testDelayedAppStart() {
   }
 
   @Test
-  public void testStartFromBackground_within100ms() {
+  public void testStartFromBackground_within50ms() {
     FakeScheduledExecutorService fakeExecutorService = new FakeScheduledExecutorService();
     Timer fakeTimer = spy(new Timer(currentTime));
     AppStartTrace trace =
         new AppStartTrace(transportManager, clock, configResolver, fakeExecutorService);
     trace.registerActivityLifecycleCallbacks(appContext);
     trace.setMainThreadRunnableTime(fakeTimer);
 
-    when(fakeTimer.getDurationMicros()).thenReturn(99L);
+    // See AppStartTrace.MAX_BACKGROUND_RUNNABLE_DELAY.
+    when(fakeTimer.getDurationMicros()).thenReturn(TimeUnit.MILLISECONDS.toMicros(50) - 1);
     trace.onActivityCreated(activity1, bundle);
     Assert.assertNotNull(trace.getOnCreateTime());
     ++currentTime;
@@ -266,15 +267,16 @@ public void testStartFromBackground_within100ms() {
   }
 
   @Test
-  public void testStartFromBackground_moreThan100ms() {
+  public void testStartFromBackground_moreThan50ms() {
     FakeScheduledExecutorService fakeExecutorService = new FakeScheduledExecutorService();
     Timer fakeTimer = spy(new Timer(currentTime));
     AppStartTrace trace =
         new AppStartTrace(transportManager, clock, configResolver, fakeExecutorService);
     trace.registerActivityLifecycleCallbacks(appContext);
     trace.setMainThreadRunnableTime(fakeTimer);
 
-    when(fakeTimer.getDurationMicros()).thenReturn(TimeUnit.MILLISECONDS.toMicros(100) + 1);
+    // See AppStartTrace.MAX_BACKGROUND_RUNNABLE_DELAY.
+    when(fakeTimer.getDurationMicros()).thenReturn(TimeUnit.MILLISECONDS.toMicros(50) + 1);
     trace.onActivityCreated(activity1, bundle);
     Assert.assertNull(trace.getOnCreateTime());
     ++currentTime;