Record UMA for battery level when precache starts and ends

BUG=646184

Review-Url: https://codereview.chromium.org/2333063002
Cr-Commit-Position: refs/heads/master@{#419337}

chrome/android/java/src/org/chromium/chrome/browser/precache/PrecacheController.java

@@ -369,6 +369,7 @@ public class PrecacheController {
                 recordPeriodicTaskIntervalHistogram();
                 cancelPrecacheCompletionTask(mAppContext);
             }
+            recordBatteryLevelAtStart();
             registerDeviceStateReceiver();
             acquirePrecachingWakeLock();
             startPrecachingAfterSyncInit();
@@ -439,6 +440,7 @@ public class PrecacheController {
         if (precachingIncomplete) {
             schedulePrecacheCompletionTask(mAppContext);
         }
+        recordBatteryLevelAtEnd();
         mHandler.removeCallbacks(mTimeoutRunnable);
         mAppContext.unregisterReceiver(mDeviceStateReceiver);
         releasePrecachingWakeLock();
@@ -543,4 +545,21 @@ public class PrecacheController {
                 .putLong(PREF_PRECACHE_PERIODIC_TASK_START_TIME_MS, current_start_time_ms)
                 .apply();
     }
+
+    private void recordBatteryLevelAtStart() {
+        mDeviceState.saveCurrentBatteryPercentage(mAppContext);
+
+        // Report battery percentage.
+        RecordHistogram.recordPercentageHistogram(
+                "Precache.BatteryPercentage.Start", mDeviceState.getSavedBatteryPercentage());
+    }
+
+    private void recordBatteryLevelAtEnd() {
+        int delta_percentage = mDeviceState.getCurrentBatteryPercentage(mAppContext)
+                - mDeviceState.getSavedBatteryPercentage();
+        if (delta_percentage >= 0) {
+            RecordHistogram.recordPercentageHistogram(
+                    "Precache.BatteryPercentageDiff.End", delta_percentage);
+        }
+    }
 }

components/precache/android/java/src/org/chromium/components/precache/DeviceState.java

@@ -17,6 +17,9 @@ import org.chromium.base.VisibleForTesting;
 public class DeviceState {
     private static DeviceState sDeviceState = null;
 
+    // Saved battery level percentage.
+    private int mSavedBatteryPercentage = 0;
+
     /** Disallow Construction of DeviceState objects. Use {@link #getInstance()} instead to create
      * a singleton instance.
      */
@@ -58,6 +61,37 @@ public class DeviceState {
                 || status == BatteryManager.BATTERY_STATUS_FULL;
     }
 
+    /**
+     * @return the previously saved battery level percentage.
+     * @param context the application context
+     */
+    public int getSavedBatteryPercentage() {
+        return mSavedBatteryPercentage;
+    }
+
+    /**
+     * Saves the current battery level percentage to be retrieved later.
+     */
+    public void saveCurrentBatteryPercentage(Context context) {
+        mSavedBatteryPercentage = getCurrentBatteryPercentage(context);
+    }
+
+    /**
+     * @return the current battery level as percentage.
+     * @param context the application context
+     */
+    public int getCurrentBatteryPercentage(Context context) {
+        IntentFilter iFilter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);
+        Intent batteryStatus = context.registerReceiver(null, iFilter);
+        if (batteryStatus == null) return 0;
+        int level = batteryStatus.getIntExtra(BatteryManager.EXTRA_LEVEL, -1);
+        int scale = batteryStatus.getIntExtra(BatteryManager.EXTRA_SCALE, -1);
+        if (level == -1 || scale == -1) return 0;
+        if (scale == 0) return 0;
+
+        return Math.round(100 * level / (float) scale);
+    }
+
     /** @return whether the currently active network is unmetered. */
     public boolean isUnmeteredNetworkAvailable(Context context) {
         NetworkInfoDelegate networkInfo =

tools/metrics/histograms/histograms.xml

@@ -45294,6 +45294,26 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Precache.BatteryPercentage.Start" units="%">
+  <owner>bengr@chromium.org</owner>
+  <owner>rajendrant@chromium.org</owner>
+  <summary>
+    The battery level in percentage when the precache task was started.
+  </summary>
+</histogram>
+
+<histogram name="Precache.BatteryPercentageDiff.End" units="%">
+  <owner>bengr@chromium.org</owner>
+  <owner>rajendrant@chromium.org</owner>
+  <summary>
+    Measures the difference between the battery level percentage when the
+    precache task is started and ended. This value indicates the possible
+    battery usage due to the precache task. Logged when the precache task ends,
+    which could be due to successful completion, time-out, error conditions, max
+    download limit exceeded, etc.
+  </summary>
+</histogram>
+
 <histogram name="Precache.CacheStatus.NonPrefetch" enum="HttpCachePattern">
   <owner>jamartin@chromium.org</owner>
   <owner>bengr@chromium.org</owner>