Refine snap scrolling on the Cards New Tab Page.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageUma.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageUma.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageUma.java
index aa41d50352aeff1b8ec8469d815ffb13d68d3e8f..5480867fcf8c70d894ca7872719143c8c1f94608 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageUma.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageUma.java
@@ -10,7 +10,6 @@ import android.support.annotation.IntDef;
 import org.chromium.base.metrics.RecordHistogram;
 import org.chromium.base.metrics.RecordUserAction;
 import org.chromium.chrome.browser.UrlConstants;
-import org.chromium.chrome.browser.ntp.cards.NewTabPageListItem;
 import org.chromium.chrome.browser.rappor.RapporServiceBridge;
 import org.chromium.chrome.browser.tab.EmptyTabObserver;
 import org.chromium.chrome.browser.tab.Tab;
@@ -71,7 +70,7 @@ public class NewTabPageUma {
      * Do not remove or change existing values other than NUM_SNIPPETS_ACTIONS. */
     @IntDef({SNIPPETS_ACTION_SHOWN, SNIPPETS_ACTION_SCROLLED, SNIPPETS_ACTION_CLICKED,
              SNIPPETS_ACTION_DISMISSED_OBSOLETE, SNIPPETS_ACTION_DISMISSED_VISITED,
-             SNIPPETS_ACTION_DISMISSED_UNVISITED, SNIPPETS_ACTION_SCROLLED_BELOW_THE_FOLD_ONCE})
+             SNIPPETS_ACTION_DISMISSED_UNVISITED})
     @Retention(RetentionPolicy.SOURCE)
     public @interface SnippetsAction {}
     /** Snippets are enabled and are being shown to the user. */
@@ -86,8 +85,8 @@ public class NewTabPageUma {
     public static final int SNIPPETS_ACTION_DISMISSED_VISITED = 4;
     /** A snippet has been swiped away, it had not been viewed by the user (on this device). */
     public static final int SNIPPETS_ACTION_DISMISSED_UNVISITED = 5;
-    /** The snippet list has been scrolled below the fold (once per NTP load). */
-    public static final int SNIPPETS_ACTION_SCROLLED_BELOW_THE_FOLD_ONCE = 6;
+    /** Obsolete. The snippet list has been scrolled below the fold (once per NTP load). */
+    // public static final int SNIPPETS_ACTION_SCROLLED_BELOW_THE_FOLD_ONCE = 6;
     /** The number of possible actions. */
     private static final int NUM_SNIPPETS_ACTIONS = 7;
 
@@ -184,44 +183,6 @@ public class NewTabPageUma {
     }
 
     /**
-     * Snap state representing which part of the NTP the user is reading.
-     */
-    public enum SnapState {
-        ABOVE_THE_FOLD,
-        BELOW_THE_FOLD,
-    }
-
-    /**
-     * Snap state observer that records UMA actions or histograms.
-     */
-    public static class SnapStateObserver {
-        private SnapState mSnapState = SnapState.ABOVE_THE_FOLD;
-        private boolean mEverBelowTheFold = false;
-
-        public void updateSnapState(NewTabPageView newTabPageView, SnapState state) {
-            if (state == mSnapState) return;
-            mSnapState = state;
-
-            switch (state) {
-                case ABOVE_THE_FOLD:
-                    RecordUserAction.record("MobileNTP.Snippets.ScrolledAboveTheFold");
-                    break;
-                case BELOW_THE_FOLD:
-                    RecordUserAction.record("MobileNTP.Snippets.ScrolledBelowTheFold");
-                    if (!mEverBelowTheFold) {
-                        mEverBelowTheFold = true;
-                        recordSnippetAction(SNIPPETS_ACTION_SCROLLED_BELOW_THE_FOLD_ONCE);
-                        RecordHistogram.recordSparseSlowlyHistogram(
-                                "NewTabPage.Snippets.NumArticlesOnScrolledBelowTheFoldOnce",
-                                newTabPageView.getViewCountMatchingViewType(
-                                        NewTabPageListItem.VIEW_TYPE_SNIPPET));
-                    }
-                    break;
-            }
-        }
-    }
-
-    /**
      * Records stats related to article visits, such as the time spent on the website, or if the
      * user comes back to the NTP. Use through {@link NewTabPageUma#monitorVisit(Tab)}.
      */