Fix three crashes in the recent tabs dialog.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/RecentTabsManager.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/RecentTabsManager.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/RecentTabsManager.java
index 445f69bf0c3a3ffc314f9e1427a938fa42983361..5f2749c02211638b11ec085e4294246f3c50e889 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/RecentTabsManager.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/RecentTabsManager.java
@@ -67,6 +67,7 @@ public class RecentTabsManager implements AndroidSyncSettingsObserver, SignInSta
     private SigninManager mSignInManager;
     private UpdatedCallback mUpdatedCallback;
     private ProfileDataCache mProfileDataCache;
+    private boolean mIsDestroyed;
 
     /**
      * Create an RecentTabsManager to be used with RecentTabsPage and RecentTabsRowAdapter.
@@ -98,6 +99,7 @@ public class RecentTabsManager implements AndroidSyncSettingsObserver, SignInSta
      * Should be called when this object is no longer needed. Performs necessary listener tear down.
      */
     public void destroy() {
+        mIsDestroyed = true;
         AndroidSyncSettings.unregisterObserver(mContext, this);
 
         mSignInManager.removeSignInStateObserver(this);
@@ -125,6 +127,13 @@ public class RecentTabsManager implements AndroidSyncSettingsObserver, SignInSta
         InvalidationController.get(mContext).onRecentTabsPageClosed();
     }
 
+    /**
+     * Returns true if destroy() has been called.
+     */
+    public boolean isDestroyed() {
+        return mIsDestroyed;
+    }
+
     private static ForeignSessionHelper buildForeignSessionHelper(Profile profile) {
         return new ForeignSessionHelper(profile);
     }
@@ -420,6 +429,7 @@ public class RecentTabsManager implements AndroidSyncSettingsObserver, SignInSta
         ThreadUtils.runOnUiThread(new Runnable() {
             @Override
             public void run() {
+                if (mIsDestroyed) return;
                 updateForeignSessions();
                 postUpdate();
                 for (AndroidSyncSettingsObserver observer : mObservers) {