Reland: 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 d934aa9b86569434e8f089c2f2c2635636510bc9..264d2e8cd6d86c806b385bcb4c557df632641521 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 +13,8 @@ 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.text.TextUtils;
 import android.view.ContextMenu;
 import android.view.LayoutInflater;
 import android.view.Menu;
@@ -22,6 +24,7 @@ import android.view.View;
 import org.chromium.base.ApiCompatibilityUtils;
 import org.chromium.base.Callback;
 import org.chromium.base.CommandLine;
+import org.chromium.base.Log;
 import org.chromium.base.ThreadUtils;
 import org.chromium.base.VisibleForTesting;
 import org.chromium.base.metrics.RecordHistogram;
@@ -70,6 +73,8 @@ 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.content_public.common.Referrer;
 import org.chromium.net.NetworkChangeNotifier;
 import org.chromium.ui.base.DeviceFormFactor;
@@ -87,6 +92,7 @@ import jp.tomorrowkey.android.gifplayer.BaseGifImage;
  */
 public class NewTabPage
         implements NativePage, InvalidationAwareThumbnailProvider, TemplateUrlServiceObserver {
+    private static final String TAG = "NewTabPage";
 
     // MostVisitedItem Context menu item IDs.
     static final int ID_OPEN_IN_NEW_WINDOW = 0;
@@ -104,6 +110,9 @@ 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 final String CHROME_CONTENT_SUGGESTIONS_REFERRER =
             "https://www.googleapis.com/auth/chrome-content-suggestions";
 
@@ -671,6 +680,29 @@ public class NewTabPage
             public void onHidden(Tab tab) {
                 if (mIsLoaded) recordNTPInteractionTime();
             }
+
+            @Override
+            public void onPageLoadStarted(Tab tab, String url) {
+                int scrollPosition = mNewTabPageView.getScrollPosition();
+                if (scrollPosition == RecyclerView.NO_POSITION) return;
+
+                if (mTab.getWebContents() == null) return;
+
+                NavigationController controller = mTab.getWebContents().getNavigationController();
+                int index = controller.getLastCommittedEntryIndex();
+                NavigationEntry entry = controller.getEntryAtIndex(index);
+                if (entry == null) return;
+
+                // At least under test conditions this method may be called initially for the load
+                // of the NTP itself, at which point the last committed entry is not for the NTP
+                // yet. This method will then be called a second time when the user navigates away,
+                // at which point the last committed entry is for the NTP. The extra data must only
+                // be set in the latter case.
+                if (!isNTPUrl(entry.getUrl())) return;
+
+                controller.setEntryExtraData(index, NAVIGATION_ENTRY_SCROLL_POSITION_KEY,
+                        Integer.toString(scrollPosition));
+            }
         };
         mTab.addObserver(mTabObserver);
         mMostVisitedSites = buildMostVisitedSites(mProfile);
@@ -683,7 +715,8 @@ public class NewTabPage
 
         LayoutInflater inflater = LayoutInflater.from(activity);
         mNewTabPageView = (NewTabPageView) inflater.inflate(R.layout.new_tab_page_view, null);
-        mNewTabPageView.initialize(mNewTabPageManager, mSearchProviderHasLogo);
+        mNewTabPageView.initialize(
+                mNewTabPageManager, mSearchProviderHasLogo, getScrollPositionFromNavigationEntry());
 
         RecordHistogram.recordBooleanHistogram(
                 "NewTabPage.MobileIsUserOnline", NetworkChangeNotifier.isOnline());
@@ -843,6 +876,29 @@ 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();
+        int index = controller.getLastCommittedEntryIndex();
+        String scrollPositionData =
+                controller.getEntryExtraData(index, NAVIGATION_ENTRY_SCROLL_POSITION_KEY);
+        if (TextUtils.isEmpty(scrollPositionData)) return RecyclerView.NO_POSITION;
+
+        try {
+            return Integer.parseInt(scrollPositionData);
+        } catch (NumberFormatException e) {
+            Log.w(TAG, "Bad data found for scroll position: %s", scrollPositionData, e);
+            return RecyclerView.NO_POSITION;
+        }
+    }
+
+    /**
      * @return Whether the NTP has finished loaded.
      */
     @VisibleForTesting