Ntp: restore scroll position.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java
index ff1a75b8513ee3d3802bcc1f495e1c046197cf08..f58f1ec0263777047363d22183aaf5445bcb87b2 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPage.java
@@ -13,6 +13,7 @@ import android.net.Uri;
 import android.os.Build;
 import android.os.SystemClock;
 import android.support.v4.view.ViewCompat;
+import android.support.v7.widget.RecyclerView;
 import android.view.ContextMenu;
 import android.view.LayoutInflater;
 import android.view.Menu;
@@ -68,6 +69,8 @@ import org.chromium.chrome.browser.tabmodel.TabModelUtils;
 import org.chromium.chrome.browser.tabmodel.document.TabDelegate;
 import org.chromium.chrome.browser.util.UrlUtilities;
 import org.chromium.content_public.browser.LoadUrlParams;
+import org.chromium.content_public.browser.NavigationController;
+import org.chromium.content_public.browser.NavigationEntry;
 import org.chromium.net.NetworkChangeNotifier;
 import org.chromium.ui.WindowOpenDisposition;
 import org.chromium.ui.base.DeviceFormFactor;
@@ -101,6 +104,9 @@ public class NewTabPage
     private static final int CTA_IMAGE_CLICKED = 1;
     private static final int ANIMATED_LOGO_CLICKED = 2;
 
+    // Key for the scroll position data that may be stored in a navigation entry.
+    private static final String NAVIGATION_ENTRY_SCROLL_POSITION_KEY = "NewTabPageScrollPosition";
+
     private static MostVisitedSites sMostVisitedSitesForTests;
 
     private final Tab mTab;
@@ -644,6 +650,16 @@ public class NewTabPage
             public void onHidden(Tab tab) {
                 if (mIsLoaded) recordNTPInteractionTime();
             }
+
+            @Override
+            public void onPageLoadStarted(Tab tab, String url) {
+                if (mTab.getWebContents() == null) return;
+
+                NavigationController controller = mTab.getWebContents().getNavigationController();
+                int index = controller.getLastCommittedEntryIndex();
+                controller.setEntryExtraData(index, NAVIGATION_ENTRY_SCROLL_POSITION_KEY,
+                        Integer.toString(mNewTabPageView.getScrollPosition()));
+            }
         };
         mTab.addObserver(mTabObserver);
         mMostVisitedSites = buildMostVisitedSites(mProfile);
@@ -656,7 +672,8 @@ public class NewTabPage
 
         LayoutInflater inflater = LayoutInflater.from(activity);
         mNewTabPageView = (NewTabPageView) inflater.inflate(R.layout.new_tab_page_view, null);
-        mNewTabPageView.initialize(mNewTabPageManager, mSearchProviderHasLogo, mSnippetsBridge);
+        mNewTabPageView.initialize(mNewTabPageManager, mSearchProviderHasLogo, mSnippetsBridge,
+                getScrollPositionFromNavigationEntry());
 
         RecordHistogram.recordBooleanHistogram(
                 "NewTabPage.MobileIsUserOnline", NetworkChangeNotifier.isOnline());
@@ -816,6 +833,29 @@ public class NewTabPage
     }
 
     /**
+     * Returns the value of the adapter scroll position that was stored in the last committed
+     * navigation entry. Returns {@code RecyclerView.NO_POSITION} if there is no last committed
+     * navigation entry, or if no data is found.
+     * @return The adapter scroll position.
+     */
+    private int getScrollPositionFromNavigationEntry() {
+        if (mTab.getWebContents() == null) return RecyclerView.NO_POSITION;
+
+        NavigationController controller = mTab.getWebContents().getNavigationController();
+        NavigationEntry entry = controller.getEntryAtIndex(controller.getLastCommittedEntryIndex());
+        if (entry == null) return RecyclerView.NO_POSITION;
+
+        String scrollPositionData = entry.getExtraData(NAVIGATION_ENTRY_SCROLL_POSITION_KEY);
+
+        try {
+            return Integer.parseInt(scrollPositionData);
+        } catch (NumberFormatException e) {
+            // Sometimes there is no data in the navigation entry.
+            return RecyclerView.NO_POSITION;
+        }
+    }
+
+    /**
      * @return Whether the NTP has finished loaded.
      */
     @VisibleForTesting