Delete NewTabPage.RecentTabsPage.TimeVisibleAndroid UMA metric

This CL deletes recording of
NewTabPage.RecentTabsPage.TimeVisibleAndroid UMA metric.

BUG=1053084

Change-Id: I2c7fa9c9c70993bec7d2a5b97bb32495a2b924a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2130889Reviewed-by: Theresa  <twellington@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755491}

chrome/android/java/src/org/chromium/chrome/browser/ntp/RecentTabsPage.java

@@ -8,7 +8,6 @@ import android.app.Activity;
 import android.content.res.Resources;
 import android.graphics.Canvas;
 import android.graphics.Color;
-import android.os.SystemClock;
 import android.view.ContextMenu;
 import android.view.ContextMenu.ContextMenuInfo;
 import android.view.LayoutInflater;
@@ -20,7 +19,6 @@ import androidx.core.view.ViewCompat;
 
 import org.chromium.base.ActivityState;
 import org.chromium.base.ApplicationStatus;
-import org.chromium.base.metrics.RecordHistogram;
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.ChromeActivity;
 import org.chromium.chrome.browser.compositor.layouts.content.InvalidationAwareThumbnailProvider;
@@ -68,13 +66,6 @@ public class RecentTabsPage
      */
     private boolean mIsAttachedToWindow;
 
-    /**
-     * The time, whichever is most recent, that the page:
-     * - Moved to the foreground
-     * - Became visible
-     */
-    private long mForegroundTimeMs;
-
     /**
      * Constructor returns an instance of RecentTabsPage.
      *
@@ -132,11 +123,7 @@ public class RecentTabsPage
 
         mInForeground = inForeground;
         if (mInForeground) {
-            mForegroundTimeMs = SystemClock.elapsedRealtime();
             mRecentTabsManager.recordRecentTabMetrics();
-        } else {
-            RecordHistogram.recordLongTimesHistogram("NewTabPage.RecentTabsPage.TimeVisibleAndroid",
-                    SystemClock.elapsedRealtime() - mForegroundTimeMs);
         }
     }
 

tools/metrics/histograms/histograms.xml

@@ -101878,6 +101878,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="NewTabPage.RecentTabsPage.TimeVisibleAndroid" units="ms"
     expires_after="M82">
+  <obsolete>
+    Removed March 2020.
+  </obsolete>
   <owner>pkotwicz@chromium.org</owner>
   <owner>treib@chromium.org</owner>
   <summary>