Only show Last N Pages in the UI when the corresponding tab is visible.

chrome/android/java/src/org/chromium/chrome/browser/offlinepages/OfflinePageBridge.java

Index: chrome/android/java/src/org/chromium/chrome/browser/offlinepages/OfflinePageBridge.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/offlinepages/OfflinePageBridge.java b/chrome/android/java/src/org/chromium/chrome/browser/offlinepages/OfflinePageBridge.java
index f2f42ff68774c0cc1a37078937f4566e626962bc..fd99d14e1dc8091e7f3710431cab16d6eeb51afd 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/offlinepages/OfflinePageBridge.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/offlinepages/OfflinePageBridge.java
@@ -26,6 +26,7 @@ import java.util.Set;
 public class OfflinePageBridge {
     public static final String ASYNC_NAMESPACE = "async_loading";
     public static final String BOOKMARK_NAMESPACE = "bookmark";
+    public static final String LAST_N_NAMESPACE = "last_n";
     public static final String SHARE_NAMESPACE = "share";
 
     /**
@@ -435,6 +436,16 @@ public class OfflinePageBridge {
         nativeCheckPagesExistOffline(mNativeOfflinePageBridge, urlArray, callbackInternal);
     }
 
+    /** Tells the native side that a new tab has been added for this profile. */
+    void registerRecentTab(int tabId) {
+        nativeRegisterRecentTab(mNativeOfflinePageBridge, tabId);
+    }
+
+    /** Tells the native side that a new tab has been removed for this profile. */
+    void unregisterRecentTab(int tabId) {
+        nativeUnregisterRecentTab(mNativeOfflinePageBridge, tabId);
+    }
+
     @VisibleForTesting
     static void setOfflineBookmarksEnabledForTesting(boolean enabled) {
         sOfflineBookmarksEnabled = enabled;
@@ -502,12 +513,13 @@ public class OfflinePageBridge {
     private static native boolean nativeIsPageSharingEnabled();
     private static native boolean nativeCanSavePage(String url);
     private static native OfflinePageBridge nativeGetOfflinePageBridgeForProfile(Profile profile);
-
     @VisibleForTesting
     native void nativeGetAllPages(long nativeOfflinePageBridge, List<OfflinePageItem> offlinePages,
             final Callback<List<OfflinePageItem>> callback);
     private native void nativeCheckPagesExistOffline(long nativeOfflinePageBridge, Object[] urls,
             CheckPagesExistOfflineCallbackInternal callback);
+    private native void nativeRegisterRecentTab(long nativeOfflinePageBridge, int tabId);
+    private native void nativeUnregisterRecentTab(long nativeOfflinePageBridge, int tabId);
     @VisibleForTesting
     native void nativeGetRequestsInQueue(
             long nativeOfflinePageBridge, Callback<SavePageRequest[]> callback);