[Feed] Save and restore instance state for the Stream

Bug: 851981
Change-Id: I2e97155353f2119661df92cdd023e2e086328d18
Reviewed-on: https://chromium-review.googlesource.com/1157441
Commit-Queue: Theresa <twellington@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585584}

chrome/android/feed/core/java/src/org/chromium/chrome/browser/feed/FeedNewTabPage.java

@@ -273,8 +273,8 @@ public class FeedNewTabPage extends NewTabPage {
     }
 
     @Override
-    protected void restoreLastScrollPosition() {
-        // This behavior is handled by the Feed library.
+    protected void saveLastScrollPosition() {
+        // This behavior is handled by the StreamLifecycleManager and the Feed library.
     }
 
     @Override

chrome/android/feed/core/java/src/org/chromium/chrome/browser/feed/FeedNewTabPageMediator.java

@@ -171,7 +171,7 @@ class FeedNewTabPageMediator
         if (!isScrollViewInitialized()) return 0;
 
         int firstChildTop = mCoordinator.getStream().getChildTopAt(0);
-        return firstChildTop != Stream.POSITION_NOT_KNOWN ? -firstChildTop : 0;
+        return firstChildTop != Stream.POSITION_NOT_KNOWN ? -firstChildTop : Integer.MIN_VALUE;
     }
 
     @Override

chrome/android/feed/core/java/src/org/chromium/chrome/browser/feed/StreamLifecycleManager.java

@@ -5,7 +5,6 @@
 package org.chromium.chrome.browser.feed;
 
 import android.app.Activity;
-import android.os.Bundle;
 import android.support.annotation.IntDef;
 
 import com.google.android.libraries.feed.api.stream.Stream;
@@ -13,9 +12,12 @@ import com.google.android.libraries.feed.api.stream.Stream;
 import org.chromium.base.ActivityState;
 import org.chromium.base.ApplicationStatus;
 import org.chromium.base.VisibleForTesting;
+import org.chromium.chrome.browser.ntp.NewTabPage;
 import org.chromium.chrome.browser.tab.EmptyTabObserver;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.tab.TabObserver;
+import org.chromium.content_public.browser.NavigationController;
+import org.chromium.content_public.browser.NavigationEntry;
 
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
@@ -29,6 +31,9 @@ class StreamLifecycleManager implements ApplicationStatus.ActivityStateListener
     @Retention(RetentionPolicy.SOURCE)
     private @interface StreamState {}
 
+    /** Key for the Stream instance state that may be stored in a navigation entry. */
+    private static final String STREAM_SAVED_INSTANCE_STATE_KEY = "StreamSavedInstanceState";
+
     private static final int NOT_SPECIFIED = -1;
     private static final int CREATED = 0;
     private static final int SHOWN = 1;
@@ -86,11 +91,15 @@ class StreamLifecycleManager implements ApplicationStatus.ActivityStateListener
             public void onHidden(Tab tab) {
                 hide();
             }
+
+            @Override
+            public void onPageLoadStarted(Tab tab, String url) {
+                saveInstanceState();
+            }
         };
 
         mStreamState = CREATED;
-        // TODO(huayinz): Handle saved instance state.
-        mStream.onCreate((Bundle) null);
+        mStream.onCreate(restoreInstanceState());
         show();
         activate();
 
@@ -166,6 +175,9 @@ class StreamLifecycleManager implements ApplicationStatus.ActivityStateListener
 
         deactivate();
         mStreamState = HIDDEN;
+        // Save instance state as the Stream begins to hide. This matches the activity lifecycle
+        // that instance state is saved as the activity begins to stop.
+        saveInstanceState();
         mStream.onHide();
     }
 
@@ -183,6 +195,37 @@ class StreamLifecycleManager implements ApplicationStatus.ActivityStateListener
         mStream.onDestroy();
     }
 
+    /** Save the Stream instance state to the navigation entry if necessary. */
+    private void saveInstanceState() {
+        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 (!NewTabPage.isNTPUrl(entry.getUrl())) return;
+
+        controller.setEntryExtraData(
+                index, STREAM_SAVED_INSTANCE_STATE_KEY, mStream.getSavedInstanceStateString());
+    }
+
+    /**
+     * @return The Stream instance state saved in navigation entry, or null if it is not previously
+     *         saved.
+     */
+    private String restoreInstanceState() {
+        if (mTab.getWebContents() == null) return null;
+
+        NavigationController controller = mTab.getWebContents().getNavigationController();
+        int index = controller.getLastCommittedEntryIndex();
+        return controller.getEntryExtraData(index, STREAM_SAVED_INSTANCE_STATE_KEY);
+    }
+
     @VisibleForTesting
     TabObserver getTabObserverForTesting() {
         return mTabObserver;

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

@@ -314,7 +314,7 @@ public class NewTabPage
 
             @Override
             public void onPageLoadStarted(Tab tab, String url) {
-                restoreLastScrollPosition();
+                saveLastScrollPosition();
             }
         };
         mTab.addObserver(mTabObserver);
@@ -349,9 +349,9 @@ public class NewTabPage
     }
 
     /**
-     * Restore the last scroll position stored in the navigation entry (if set).
+     * Save the last scroll position stored in the navigation entry if necessary.
      */
-    protected void restoreLastScrollPosition() {
+    protected void saveLastScrollPosition() {
         int scrollPosition = mNewTabPageView.getScrollPosition();
         if (scrollPosition == RecyclerView.NO_POSITION) return;
 

chrome/android/junit/src/org/chromium/chrome/browser/feed/StreamLifecycleManagerTest.java

@@ -12,7 +12,6 @@ import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 import android.app.Activity;
-import android.os.Bundle;
 import android.support.test.filters.SmallTest;
 
 import com.google.android.libraries.feed.api.stream.Stream;
@@ -51,7 +50,7 @@ public class StreamLifecycleManagerTest {
         MockitoAnnotations.initMocks(this);
         ApplicationStatus.onStateChangeForTesting(mActivity, ActivityState.CREATED);
         mStreamLifecycleManager = new StreamLifecycleManager(mStream, mActivity, mTab);
-        verify(mStream, times(1)).onCreate(or(any(Bundle.class), isNull()));
+        verify(mStream, times(1)).onCreate(or(any(String.class), isNull()));
     }
 
     @Test