No issue: remove unused HotStartPerformanceMonitor.

This monitor for hot start was intended to be used by FNPRMS to measure
hot start. However, hot start was deprioritized so it's now essentially
unused.

app/src/main/java/org/mozilla/fenix/HomeActivity.kt

@@ -59,7 +59,6 @@ import org.mozilla.fenix.home.intent.SpeechProcessingIntentProcessor
 import org.mozilla.fenix.home.intent.StartSearchIntentProcessor
 import org.mozilla.fenix.library.bookmarks.BookmarkFragmentDirections
 import org.mozilla.fenix.library.history.HistoryFragmentDirections
-import org.mozilla.fenix.perf.HotStartPerformanceMonitor
 import org.mozilla.fenix.perf.Performance
 import org.mozilla.fenix.perf.StartupTimeline
 import org.mozilla.fenix.search.SearchFragmentDirections
@@ -86,8 +85,6 @@ open class HomeActivity : LocaleAwareAppCompatActivity() {
 
     private var sessionObserver: SessionManager.Observer? = null
 
-    private val hotStartMonitor = HotStartPerformanceMonitor()
-
     private var isToolbarInflated = false
 
     private val webExtensionPopupFeature by lazy {
@@ -161,16 +158,6 @@ open class HomeActivity : LocaleAwareAppCompatActivity() {
         }
     }
 
-    final override fun onRestart() {
-        hotStartMonitor.onRestartFirstMethodCall()
-        super.onRestart()
-    }
-
-    final override fun onPostResume() {
-        super.onPostResume()
-        hotStartMonitor.onPostResumeFinalMethodCall()
-    }
-
     final override fun onPause() {
         super.onPause()
 

app/src/main/java/org/mozilla/fenix/perf/HotStartPerformanceMonitor.kt

@@ -1,46 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-package org.mozilla.fenix.perf
-
-import android.os.SystemClock
-import android.util.Log
-
-/**
- * Monitors and reports elapsed time to complete hot startup of an Activity. Callers are expected
- * to call the appropriate lifecycle methods at the appropriate times.
- *
- * A "hot startup" is when the application moves from the background to the foreground and both the
- * Application/process and the Activity under measurement are already created.
- *
- * Unfortunately, this monitor does not capture the entire duration of hot start because the
- * framework calls several Android framework methods in the application's process before we are able
- * to add monitoring code (i.e. the first time our application code is called in onRestart). An
- * alternative implementation could measure performance from outside the application.
- *
- * The logs from this class are not visible to users by default. To see logs from this class, the
- * user must enable VERBOSE logging for the appropriate tag:
- *   adb shell setprop log.tag.FenixPerf VERBOSE
- */
-class HotStartPerformanceMonitor(
-    // We use VERBOSE logging so that the logs are not visible to users by default. We use the
-    // Android Log methods to minimize overhead introduced in a-c logging.
-    private val log: (String) -> Unit = { Log.v(Performance.TAG, it) },
-    private val getElapsedRealtime: () -> Long = { SystemClock.elapsedRealtime() }
-) {
-
-    private var onRestartMillis: Long = -1
-
-    fun onRestartFirstMethodCall() {
-        onRestartMillis = getElapsedRealtime()
-    }
-
-    fun onPostResumeFinalMethodCall() {
-        // If onRestart was never called, this is not a hot start: ignore it.
-        if (onRestartMillis >= 0) {
-            val elapsedMillis = getElapsedRealtime() - onRestartMillis
-            log("hot start: $elapsedMillis")
-        }
-    }
-}

app/src/test/java/org/mozilla/fenix/perf/HotStartPerformanceMonitorTest.kt

@@ -1,43 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-package org.mozilla.fenix.perf
-
-import io.mockk.Called
-import io.mockk.MockKAnnotations
-import io.mockk.impl.annotations.MockK
-import io.mockk.verify
-import org.junit.Before
-import org.junit.Test
-
-class HotStartPerformanceMonitorTest {
-
-    private lateinit var monitor: HotStartPerformanceMonitor
-
-    @MockK(relaxed = true) private lateinit var log: (String) -> Unit
-    private var elapsedRealtime = 0L
-
-    @Before
-    fun setUp() {
-        MockKAnnotations.init(this)
-        monitor = HotStartPerformanceMonitor(log, getElapsedRealtime = { elapsedRealtime })
-    }
-
-    @Test
-    fun `WHEN onRestart is not called but onPostResume is called THEN we do not log`() {
-        monitor.onPostResumeFinalMethodCall()
-        verify { log.invoke(any()) wasNot Called }
-    }
-
-    @Test
-    fun `WHEN onRestart then onPostResume is called THEN we log the elapsed time`() {
-        elapsedRealtime = 10
-        monitor.onRestartFirstMethodCall()
-
-        elapsedRealtime = 100
-        monitor.onPostResumeFinalMethodCall()
-
-        verify { log.invoke("hot start: 90") } // fragile but it's not worth the time to make robust.
-    }
-}