weblayer: Record Session.TotalDuration

Simple copy of chrome on android's implementation, using the
equivalent activity lifecycle callbacks. All done in java.

Bug: 1143945
Change-Id: Icae399db1c64c5cb872de18f2673270625d7679e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510371Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822779}

weblayer/browser/java/org/chromium/weblayer_private/BrowserFragmentImpl.java

@@ -8,12 +8,14 @@ import android.app.Activity;
 import android.content.Context;
 import android.content.Intent;
 import android.os.Bundle;
+import android.os.SystemClock;
 import android.view.ContextThemeWrapper;
 import android.view.View;
 import android.view.ViewGroup;
 
 import androidx.annotation.Nullable;
 
+import org.chromium.base.metrics.RecordHistogram;
 import org.chromium.components.browser_ui.styles.R;
 import org.chromium.components.embedder_support.application.ClassLoaderContextWrapperFactory;
 import org.chromium.weblayer_private.interfaces.BrowserFragmentArgs;
@@ -27,6 +29,9 @@ import org.chromium.weblayer_private.interfaces.StrictModeWorkaround;
  * Implementation of RemoteFragmentImpl which forwards logic to BrowserImpl.
  */
 public class BrowserFragmentImpl extends RemoteFragmentImpl {
+    private static int sResumedCount;
+    private static long sSessionStartTimeMs;
+
     private final ProfileImpl mProfile;
     private final String mPersistenceId;
 
@@ -137,12 +142,19 @@ public class BrowserFragmentImpl extends RemoteFragmentImpl {
     @Override
     public void onResume() {
         super.onResume();
+        sResumedCount++;
+        if (sResumedCount == 1) sSessionStartTimeMs = SystemClock.uptimeMillis();
         mBrowser.onFragmentResume();
     }
 
     @Override
     public void onPause() {
         super.onPause();
+        sResumedCount--;
+        if (sResumedCount == 0) {
+            long deltaMs = SystemClock.uptimeMillis() - sSessionStartTimeMs;
+            RecordHistogram.recordLongTimesHistogram("Session.TotalDuration", deltaMs);
+        }
         mBrowser.onFragmentPause();
     }