feat(macrobenchmark): Measure SentryAndroid.init as its own metric

SentryAndroid.init wraps itself in an android.os.Trace section (#5901), and
macrobenchmark sets atrace_apps=["*"] on API 29+, so the section reaches the
perfetto trace on the api-35 device we run. TraceSectionMetric turns it into a
reported metric.

This is the metric worth watching: timeToInitialDisplay measures the whole cold
start, so an SDK-init change has to be tens of milliseconds to clear the noise,
while this isolates init itself.

Author: runningcode

sentry-android-integration-tests/sentry-uitest-android-macrobenchmark/src/main/java/io/sentry/uitest/android/macrobenchmark/SentryStartupBenchmark.kt

@@ -2,8 +2,10 @@ package io.sentry.uitest.android.macrobenchmark
 
 import android.util.Log
 import androidx.benchmark.macro.CompilationMode
+import androidx.benchmark.macro.ExperimentalMetricApi
 import androidx.benchmark.macro.StartupMode
 import androidx.benchmark.macro.StartupTimingMetric
+import androidx.benchmark.macro.TraceSectionMetric
 import androidx.benchmark.macro.junit4.MacrobenchmarkRule
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import androidx.test.platform.app.InstrumentationRegistry
@@ -33,11 +35,17 @@ class SentryStartupBenchmark {
 
   @get:Rule val benchmarkRule = MacrobenchmarkRule()
 
+  @OptIn(ExperimentalMetricApi::class)
   @Test
   fun startupFullCompilation() =
     benchmarkRule.measureRepeated(
       packageName = TARGET_PACKAGE,
-      metrics = listOf(StartupTimingMetric()),
+      // TraceSectionMetric picks up the android.os.Trace section SentryAndroid.init wraps
+      // itself in. The sample app auto-inits from its ContentProvider, so this lands inside
+      // the cold-start window being measured. Unlike timeToInitialDisplay this isolates SDK
+      // startup from the rest of the app, so a regression shows up without having to clear
+      // cold-start noise.
+      metrics = listOf(StartupTimingMetric(), TraceSectionMetric(SENTRY_INIT_SECTION)),
       compilationMode = CompilationMode.Full(),
       startupMode = StartupMode.COLD,
       iterations = 12,
@@ -48,6 +56,10 @@ class SentryStartupBenchmark {
 
   companion object {
     private const val TARGET_PACKAGE = "io.sentry.samples.android"
+
+    /** Matches the `Trace.beginSection` name in `SentryAndroid.init`. */
+    private const val SENTRY_INIT_SECTION = "SentryAndroid.init"
+
     private const val BENCHMARK_DATA_SUFFIX = "-benchmarkData.json"
 
     /** Kept in sync with `scripts/parse-macrobenchmark-log.py`. */