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 f5b0d2773ef74a89c6ead1aa7607ea08107cd4f1..c9b2f1f78c08e34bc4a6fbcd1bf176ed577faa15 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;
@@ -69,6 +70,8 @@ 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.WindowOpenDisposition;
@@ -103,6 +106,9 @@ 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";
 
@@ -665,6 +671,16 @@ 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();

[Ted C, 2016/09/19 19:59:08]

I would add an assert here that controller.getEntryAtIndex(index).getUrl() is an
NTP URL just to make sure we don't ever mix this up.

[Michael van Ouwerkerk, 2016/09/20 11:08:16]

Done.

+                controller.setEntryExtraData(index, NAVIGATION_ENTRY_SCROLL_POSITION_KEY,
+                        Integer.toString(mNewTabPageView.getScrollPosition()));
+            }
         };
         mTab.addObserver(mTabObserver);
         mMostVisitedSites = buildMostVisitedSites(mProfile);
@@ -677,7 +693,8 @@ 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());
@@ -837,6 +854,29 @@ 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);

[Ted C, 2016/09/19 19:59:08]

I would check for null here and then make the exception handler be a case where
an error actually occurred (where invalid data was stored for some reason).

[Michael van Ouwerkerk, 2016/09/20 11:08:16]

Done.

+
+        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