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..977d56b11b12ee5309020ae3588fb3fcfa94ed10 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
@@ -101,6 +101,9 @@ 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 +647,12 @@ public class NewTabPage
             public void onHidden(Tab tab) {
                 if (mIsLoaded) recordNTPInteractionTime();
             }
+
+            @Override
+            public void onPageLoadStarted(Tab tab, String url) {
+                mTab.setLastCommittedNavigationEntryExtraData(NAVIGATION_ENTRY_SCROLL_POSITION_KEY,
+                        Integer.toString(mNewTabPageView.getScrollPosition()));
+            }
         };
         mTab.addObserver(mTabObserver);
         mMostVisitedSites = buildMostVisitedSites(mProfile);
@@ -656,7 +665,8 @@ 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());
@@ -815,6 +825,17 @@ public class NewTabPage
                 "NewTabPage.TimeSpent", System.nanoTime() - mLastShownTimeNs, TimeUnit.NANOSECONDS);
     }
 
+    private int getScrollPositionFromNavigationEntry() {
+        String scrollPositionData =
+                mTab.getLastCommittedNavigationEntryExtraData(NAVIGATION_ENTRY_SCROLL_POSITION_KEY);
+        try {
+            return Integer.parseInt(scrollPositionData);
+        } catch (NumberFormatException e) {
+            // Sometimes there is no data in the navigation entry.
+            return 0;

[Bernhard Bauer, 2016/09/16 15:02:50]

Would it be slightly nicer to return NO_POSITION here to indicate the absence of
a value?

[Michael van Ouwerkerk, 2016/09/16 16:35:05]

Done.

+        }
+    }
+
     /**
      * @return Whether the NTP has finished loaded.
      */