Fix Stability.iOS.UTE.HasPossibleExplanation logging condition

Previously Stability.iOS.UTE.HasPossibleExplanation would always be true
if OSRestartedAfterPreviousSession is true. But according to M78 UMA
OSRestartedAfterPreviousSession is true in more than 50% of UTEs, which
suggests that most restarts don't actually cause UTE.

Relax the logic to take into account OSRestartedAfterPreviousSession
only if battery level at 1%.

Also remove deviceWasInLowPowerMode from logging condition as it seem
irrelevant.

Bug: 1006928
Change-Id: I583f0aaeff842ea058a54315dd27d79537242296
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1819884Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
Auto-Submit: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699377}

ios/chrome/browser/metrics/mobile_session_shutdown_metrics_provider.h

@@ -27,6 +27,11 @@ enum MobileSessionShutdownType {
   MOBILE_SESSION_SHUTDOWN_TYPE_COUNT,
 };
 
+// Percentage of battery level which is assumed low enough to have possibly
+// been the reason for the previous session ending in an unclean shutdown.
+// Percent rpresented by a value between 0 and 1.
+extern const float kCriticallyLowBatteryLevel;
+
 class MobileSessionShutdownMetricsProvider : public metrics::MetricsProvider {
  public:
   explicit MobileSessionShutdownMetricsProvider(

ios/chrome/browser/metrics/mobile_session_shutdown_metrics_provider.mm

@@ -110,6 +110,8 @@ void LogDeviceThermalState(DeviceThermalState thermal_state) {
 }
 }  // namespace
 
+const float kCriticallyLowBatteryLevel = 0.01;
+
 MobileSessionShutdownMetricsProvider::MobileSessionShutdownMetricsProvider(
     metrics::MetricsService* metrics_service)
     : metrics_service_(metrics_service) {
@@ -172,15 +174,15 @@ void MobileSessionShutdownMetricsProvider::ProvidePreviousSessionData(
   bool possible_explanation =
       // Log any of the following cases as a possible explanation for the
       // crash:
+      // - device restarted while the battery was critically low
+      (session_info.deviceBatteryState == DeviceBatteryState::kUnplugged &&
+       session_info.deviceBatteryLevel <= kCriticallyLowBatteryLevel &&
+       session_info.OSRestartedAfterPreviousSession) ||
       // - storage was critically low
       (session_info.availableDeviceStorage >= 0 &&
        session_info.availableDeviceStorage <= kCriticallyLowDeviceStorage) ||
       // - OS version changed
       session_info.isFirstSessionAfterOSUpgrade ||
-      // - OS was restarted
-      session_info.OSRestartedAfterPreviousSession ||
-      // - low power mode enabled
-      session_info.deviceWasInLowPowerMode ||
       // - device in abnormal thermal state
       session_info.deviceThermalState == DeviceThermalState::kCritical ||
       session_info.deviceThermalState == DeviceThermalState::kSerious;

ios/chrome/browser/metrics/mobile_session_shutdown_metrics_provider_unittest.mm

@@ -206,7 +206,10 @@ TEST_F(MobileSessionShutdownMetricsProviderTest,
       "Stability.iOS.UTE.HasPossibleExplanation", false, 1);
 
   // Test UTE with low battery when OS did not restart.
-  [PreviousSessionInfo sharedInstance].deviceBatteryLevel = 0.01;
+  [PreviousSessionInfo sharedInstance].deviceBatteryLevel =
+      kCriticallyLowBatteryLevel;
+  [PreviousSessionInfo sharedInstance].deviceBatteryState =
+      previous_session_info_constants::DeviceBatteryState::kUnplugged;
   histogram_tester = std::make_unique<base::HistogramTester>();
   metrics_provider_->ProvidePreviousSessionData(nullptr);
   histogram_tester->ExpectUniqueSample(
@@ -222,6 +225,15 @@ TEST_F(MobileSessionShutdownMetricsProviderTest,
       "Stability.iOS.UTE.OSRestartedAfterPreviousSession", true, 1);
   histogram_tester->ExpectUniqueSample(
       "Stability.iOS.UTE.HasPossibleExplanation", true, 1);
+
+  // Test UTE with normal battery when OS restarted after previous session.
+  [PreviousSessionInfo sharedInstance].deviceBatteryLevel = 50;
+  histogram_tester = std::make_unique<base::HistogramTester>();
+  metrics_provider_->ProvidePreviousSessionData(nullptr);
+  histogram_tester->ExpectUniqueSample(
+      "Stability.iOS.UTE.OSRestartedAfterPreviousSession", true, 1);
+  histogram_tester->ExpectUniqueSample(
+      "Stability.iOS.UTE.HasPossibleExplanation", false, 1);
 }
 
 INSTANTIATE_TEST_SUITE_P(/* No InstantiationName */,

ios/chrome/browser/metrics/previous_session_info_private.h

@@ -11,6 +11,8 @@
 @property(nonatomic, assign) BOOL didSeeMemoryWarningShortlyBeforeTerminating;
 @property(nonatomic, assign) BOOL isFirstSessionAfterUpgrade;
 @property(nonatomic, assign) float deviceBatteryLevel;
+@property(nonatomic, assign)
+    previous_session_info_constants::DeviceBatteryState deviceBatteryState;
 @property(nonatomic, assign) BOOL OSRestartedAfterPreviousSession;
 
 + (void)resetSharedInstanceForTesting;